I played a MP game last night; I was able to win by setting up Starbases at planets/wells that I saw my oppoent moving towards (as he was moving towards it, after he had bypassed an already contructed Starbase/well). The damage and antimatter reduction was just not enough of a deterent, he had lots of robotic crusers with him, and the antimatter came back fast enough.
I ended up putting Starbases at half my planets; I just put 1 Frigate factory at each planet, and whichever one I saw him heading for, I purchases a Starbase constructor, and the SB was being built as he entered the well. Seemed really spammy and cheep, and made the starbases seem less "special", but it worked.
BUT, I do wish my original starbase, the one I first put at my choke point, had been worth all the time/money, cause he just cruised on by it, and the penalty (-30%/-100%) did'nt seem to effect him too much. If I had to build Starbase constructors from a Cap-Ship factory, that might have made a bit of difference in my SB defence spamming. Or if they took more cap, or were more expensive, OR if Starbase starteed out with 4 slots (and could be upgraded to 6, then 8).