Yes, more structures is what this game needs...

Although I seem to remember some talk a while back of large slow mechs who were effective against structures.

I picked 100 000km range as not to force the silo to be built on the next island of the attackee. Once I get home I'll check the map and change it to more reasonable number.

// Changed it now. 50k seems reasonable.

Not 3 islands away, with 50km range, it would be 2 islands away at best and also don't forget that in order for the launching facility to have targets, you would need to have a radar located within 15km of the targets you plan to shoot. With so short range, radar would have to be on the other side of the teleport or right on the same island.

Attackers would effectively need to defend:
1) Radar(s)
2) Missile Facilities
3) The Scarabs ON THE OPEN FIELD that are carrying ammunition from terminal to launch facility(as mentioned earlier, the terminal would be ~3km from the facility).

Also worth mentioning is that these facilities will most likely not be very well fortified. This can be tweaked by setting all kinds of range restrictions on the radar and launch facilities.

As for the damage that one shot does: It should be small damage and slow cycle time to give the targets enough time to react, find facilities and mount an attack. If the cycle time is 10 minutes and each turrent takes about 6 shots to take down, it would already give targets almost an hour before any actual damage is done.

What stops from someone just building and reinforcing a bunch of radars and facilities? Nothing, really. But it has to be tweaked so it is just not worth the effort. Having a 3km no-build no-terraform radius around the buildings(due to "interference" or whatnot that fits into the lore) would make the area just way too big to reinforce properly(would be about 10km stretch that needs defences).

how do you prevent this from being used defensively.

What I would like to see in this arena is NEW bots to takes these roles.

Either New Heavy Mechs or (new class) Super Heavy Mechs !!

They would have Large weapons that would only be able to target (stationary Targets) or targets being marked with in game target markers.

Target markers would allow these large weapons to shoot at really long optimal range 1.5k +

Large weapons should have a huge hit dispersion making them useless against anything other that a building

Could go as far as to require several mods to make these guns work
     Example: Scout bot has to have a signal detector target marker to spot the target location
                    But Also the Scout needs to have a targeting relay to feed the location information to the shooter

This would work well for attacking bases..the inter island missiles sound cool also i just think the current mechanics would not allow for it with out huge revisions in the code and how the islands are viewed from the coding level.

I understand it fine, I just don't understand why having bots to perform this role isn't preferable in every way?

common tactic in supreme commander - if you can't get your units through your opponents defenses, you start to nuke him, until hi runs out of interceptor missiles.

same as in that game - the first who gets a missile through, has won the game.
This will break down to add artifical, unlogical rules, like nukes not beeing able to kill terminals or production facilities, only defense turrets (what the heck is a turrent?)

-1

This could work provided there where also bots able to perform the same task to a lesser degree; a glider with a bloody huge rocket rack(needing defenders, scouts/target markers, etc)? 

There is also the posibility of adding things like Cluster Missiles to damage a wide area(get these going and chew through the repair node accumulator before the siege bots arrive), Agent Orenge Bombs(oh look, I found your Noralgis fields... pity they don't have the anti-missile disruption that Outposts have...), E-War Missiles(dumps payload of proximity probes over a large area), Bunker Busters(see that teraformed wall with no buildings on it... flattened).

Keep the hard fighting on the side of the bots but make the missile silo a good way to maintain ongoing hostile activity that will require maintenance.

Bots are too temporary the way they are now. They can easily log out in few minutes and then they are gone from the field and in total safety. With structures, the whole operation becomes harder and more meaningful. It also gives the side that is being targeted more options on what to attack and disable. They can go after radars which is most likely closest and easiest point or they can go after the main facility. There are more options of course.

I don't mean that bots shouldn't be able to perform similar actions by themselves at all, Tux's idea on having 1.5-2km range bots coupled with target markers is awesome but suffers from the same faith: very temporary. Easily killed, easily logged to safety, easily replaced. Good idea non-the-less.

In your previous post you said like I have something against ground PVP but you didn't realise that such changes actually increase gamma ground PVP tremendously. Right now, we have couple of gamma islands that are really hard to siege. People have gone all-in on securing the island because who wants to have their huge investment and central bank destroyed. With the new structures there would be more points of interest and with the restrictions mentioned in the first post, assaults done to them would be a lot more effective than what gamma fights are right now.

Also, as mentioned in the first post, missiles would not be used to tear down the whole enemies base but to only make a hole in their defences perimeters.

well we waited how long for TFing to come into this game? Yeah im not holding much hope for proper siege mechanics for a very long time (years)

True Pros make a Podcast to influence the Devs minds, 
The rest of you guys are Hacks

PS. I got my Highways & stopped playing b4 they came in & have never used them! ...... Irony much ?

And that's why the buildings are better - they are'nt moving.

Now look what we have - ark-shoot mechanics developed for artilery, terraforming, buildings, interzone beacons. Mix all that together, shake it, add or repaint meshes - and voila! - put it on the test server for balancing.