Sorry for the late reply.
Standalone is just a way of saying the game has to be enjoyable even if you're not importing a prior Shep from ME1 or ME2. So we can assume that whatever advantage might have come from keeping the base will be compensated in some other way. Possibly more Alliance/Council support if you destroyed it, more Cerberus support if you kept it, etc...
Speculating from what "current events" are talked about in the Cerberus daily news, the galaxy seems less united than ever; this works to the Reapers' advantage.
It looks like things are shaping towards ME3 being about forming alliances, with Shepard travelling all over to accomplish missions that will gain him allies against the Reapers, as opposed to gathering a crew for a "suicide mission". Legion (Geth), Tali(Quarians), Grunt/Wrex(Krogans) are obvious candidates for "facilitators" in this search for allies. Others enjoy a certain credibility within their own factions, or have connections allowing them to co-opt these factions' resources: Samara/Liara(Asari), Miranda/Jacob(Cerberus), Ashley/Kaidan(Alliance), Mordin(Salarians). They may come back as contacts/mission introducers, providing dialogue interactions and cutscenes (perhaps some romantic ones in certain cases) without returning as squadmates. Just provide a new placeholder guy/gal for whoever's dead, so you can still get the mission even if you're missing out on some long-awaited closure.
Other characters do not offer obvious lead-ins for allies gathering: Jack, Zaeed, Kasumi, Thane and Garrus(C-Sec? It sounds like he's burned bridges there but who knows?); but they're talented people in their own fields so they could be returning squaddies in ME3. Mmm... A pirate, a merc, a thief and an assassin... sounds like a pretty good shadow-ops team to me!
It would be bringing down the number of squaddies and possibly give them more room for character development. As for the "facilitators" you get at least 2 good convos/cutscenes with each (one for introducing the mission, one at the end), with possibly another one after each new ally species is aquired (they can gather with Anderson at the Citadel) and a private meeting with LI on the Citadel before the final mission.
Samara: "Councilor Anderson is an honorable man, Shepard. I am glad my order can help other species in this worthy cause."
Shepard: "He's a good man. He's taught me a lot as my captain on the old Normandy. I'm glad you could join us here on the Citadel, but the Normandy's port observation deck feels empty without you..."
Samara: "Such feelings are irrelevant, Shepard... but they are most welcome nonetheless.<smile>. I shall assist the Councillor in organizing our defenses here. I look forward to your safe return."