Pretty off-topic at this point, but I still want to have a Vorcha squadmate. I mean, talk about a handy race to have if you're going into the Unknown. They don't live long, but they've proven to be capable of being very smart ("I may be ambitious, but I'm not crazy."), they are extremely resilent if not immune to a lot of very toxic radiation and diseases. The regeneration is annoying at times as Shep (though I admire them for it,) and they are pretty vicious in combat. I would love if SP got a Vorcha squadmate and MP allowed you to play as a Vorcha. That would be a lot of fun. 
This is why I think both gameplay modes can live in harmony. If someone wants to walk into the shoes of a Turian or Quarian or Asari, MP allows players to expand, yes expand, their RP experience. Some have talked about that they felt like they knew the lore and the story even more because they experienced the MP maps in the shoes of someone other than the Mighty Shepard.
This also gives design team some freedom to play around with difference races for the player outside of MP. The one area that I think the SP and MP team really overlaps seems to be the art design. Without SP and the lore that it brings, we wouldn't care as much about finding the Vorcha awesome, or asking to be a Krogan Female Battlemaster, which I have done and that would get me into MP in a heartbeat. Krogan are awesome, female Krogan are the best. 
Without MP, MESP probably wouldn't be as complete of a story in my opinion. The non-heroes of the story get their chance to shine, and makes those mentioned "strike teams" something the player can take part in. Without MESP, the MP side of it would be an alien shooter with a pretty bare bones plot. I know the ME series plot has been discussed, dissected and pretty much taken entirely apart. I don't think we'd be doing those things in either "camp" if it hadn't meant something to us somehow. Even with the folks that now hate the series for various reasons, it's obvious it meant enough to them that they still discuss and debate about it years later.
Both gameplay modes make for a stronger game for the ME series. I'm glad to see that so many people felt strongly enough to play the series and keep playing the series no matter what. 
I always figured that....
MESP: the story from Shepard's point-of-view.
MEMP: the story from the POV as a grunt on the front lines.
The MEMP allowed people to experience the epic battles that were largely absent from the SP experience. As for people blubbering that the inclusion of SP or MP will steal away precious dev time from their preferred game mode, the BSN is very good at pointing the finger at various elements of the game and blaming them for the experience not being everything they wanted it to be. PC players blame console players, straight people blame the inclusion of gay characters, romance arcs are blamed for taking away from the "important parts," ect. Seriously, if I hear one more dingbat claim that DAI sucked because they spent all their time writing Krem, I shall set the house on fire.
In any case, I just want a good SP story, and you don't need tons of money to pull that off. If the story blows (again), I doubt it will have anything to do with MP, and everything to do with, ya know, the writers.