Katja,
I think in your circumstances it would be proper and correct for you to use the elite lane. I would also wager that anyone who didn't think it was ok has never been in a wheelchair. I was, for a *very* short period after a knee surgery went bad. I realize this is nothing compared to your day-to-day life, but it showed me 27-gazillion other related issues that go with a mobility impairment.
On a related note, when I cleared customs the other day I noticed that the "special services" line was where all passengers in wheelchairs were taken or directed.