I don't know your playing style, but I generally capture all my planets, so that tends to suffice the need for supply for the transports and provides eventual accessibility to all planets.
These ships are shot up pretty bad when they're sent alone, and if they're destroyed they are expensive to replace, especially when they're such a specific unit. When you're at the point of having a great economy, building a few of these wouldn't be too bad, but then their ship cap of three prevents you from bolstering their numbers lest you opt for the higher tiers, which is all the reason to turn to transports and bombers again because they become more expendable and have a higher ship cap.
Thanks for the reply!
Well, as far as playing style, I tend to capture most, if not all, of my planets too. Lately I have been playing on Tree maps, which means that for most of my planets, if I raid a system ahead, I can blow up the command station, and then the planet I'm attacking is out of supply.
Like this:
(ME) --- (Missing Station) --- (To Be Raided)
So once the planet To Be Raided gets it's command station blown up (a lot easier with Raid starships then transports due to being out of my supply), the one called Missing Station will be out of the AI's supply. That means no turrets (except core) will work. Then I send my main fleet in, and mop up with very low losses. Then the one that used to be To Be Raided becomes the new Missing Station, and I raid the next one. That way, my ships mostly only attack planets that are already out of supply.
Even on maps where that doesn't work, they are amazing for things like deep strikes, taking out data centers, that sort of thing. In one game, in a Simple Normal map type, I sent my raid starships (all 9 of them that is) first to a co-processor that was 4 jumps away (through some low levels and a single mk3), blew it up, went 2 jumps up, blew up a data center, went another two jumps, into a black holed system (transports can't leave them, but raids can), blew another data center, and then returned to safety via two more jumps. Total systems visited that were not mine: 10. One trip. Of the 9 I sent out, I got 8 back, having lost a single Mk1. Why did that work so well? Part of it is because that several jumps from your lines, they actually have very few ships guarding them, and thus very little to shoot at your ships with. And the other part is just that raid starships take very little damage in general, assuming they are used for raids, sending them in to take out a single target (command station, data center, etc), or several specific targets (guard posts, spec posts, etc).
To take out a single target, rally points inside the target system in the general area of the target are good. Then, once the raid starships enter the system, you give them the order to attack that exact target. Then hold shift, and either queue up the next target, or a return to your system, or hold shift and Z and X and then click outside all the red circles, so they will fly to safety after blowing the target.
These are very micro-intense ships, and should not be considered anything otherwise. They aren't for attacking ships, although, that being said, they are super fast, and actually do pretty good damage to single targets, so they can be handy for catching lone ships, or starships that have escaped the wormhole blob.
As far as your comment about the higher tiers, and the more ship cap, while the T3 ones do survive a lot more then the tier 1 ships do, having more ships spreads out the fire the AI sends your way among more ships. If you send in just 3 T3 ships on a big raid, you are likely to lose one. Sending in all 9, likely none at all, plus the target dies faster. If you do lose one, it will be a T1, which is cheaper. As far as the mark 1's go, I do tend to agree, they aren't very good on their own.... Mostly.... For really deep raiding, if you can get them out past the hordes to the less defended areas early in the game, they could do some damage. But in general, I would say raid starships are one of those ones where unless you are planning to unlock the whole line, I wouldn't bother with them. Early game they aren't as good as mid game. Late game, they are okay.... But you lose them (often lots) going against core planets. It can be worth it though....