Seems like a fair amount. If a track gets plenty of play over your lifetime then you'll listen to it _way_ more than 99 times. If you only listen to it once, then it probably doesn't deserve more than that.
I don't think it's a good limitation to put on the accounts. Most people aren't going to upgrade (they'll just play the song on YouTube or download it), and artists are losing out on money from plays and potential fans.
I estimated my top playing artist at 6000 listens. That's max $60 on Spotify. I have paid for more than that in albums over the years.
That's just me, of course, but I'm trying to give some perspective.
While it may not add up to much for small, independent bands, at least they're getting their albums out there to a much larger audience. I know I've discovered bands I wouldn't have bothered to download if it wasn't for these services.