I'm just going to say "I disagree on many points."
I really don't think PLing is the evil you're describing. Honestly, I think a lot of us *have* seen the content on other levels and have done it to death. (I know I have. And I normally play through fairly regularly - it's one of the reasons I don't do much redside, there's just less variety there.) Also, don't assume "PLing" is "PLing to 50." There are levels, for instance, I *hate* dealing with on a mastermind and will pass by - and pick up again in the mid-late 20s. People will play how and where they want.
What we have to keep in mind with all this is that we have a *small, volunteer* team - one that's doing a damn good job, but still a small volunteer team. We saw population drops on live when we had a full time, dedicated team as well, but they came back more frequently because issues (with content, new powersets, new ATs, etc.) came out more frequently.
We're *just* seeing "issue 27" in beta right now.
Expecting tens of thousands on all the time (or even multiple thousands) for long stretches, as it sits right now, is a pipe dream. If someone won the lottery, flat out bought the COH IP for whatever NC wanted to charge for it, said "Hey, homecoming team, how would you like to make this your job," hired more staff so we could have parallel development teams and could guarantee (say) 2-3 issues a year... we'd still see drops between them. More population, sure, but we'd still see drops.
For me, right now, my main reason to return is RP. I'm on less during the weeknights - maybe joining an MSR or hami, or running a mission or three - but I'm guaranteed to be around Saturday nights, most weeks. SG night's sacred.