I've been running a 65" Hitachi rear projection for over 6 years.  It's been a great TV.  Like you, I originally had it in a large room with the seating far away from the TV (over 15 feet).  It was a room that traditionally was darker with limited windows (hence bright sunlight).  Worked awesome.
Then I moved.  Seating is closer to it now and a whole wall of windows that face NW so setting sunlight is plentiful.  You are right about it not being as bright as a plasma or LCD.  What we did was put some fabric blinds on the windows.  They are not black-out blinds, but knock the sunlight down.  It makes a big difference.  Still very light in the room via the sun, but it made a big difference in screen visibility and reflections.  It really isn't a problem viewing the screen anymore.
My major issue is my rptv is older so it's pretty deep.  The front of the TV sits a good 38 inches from the wall.  That's a lot of floor space one is giving up.  Especially in a room much smaller than one in the previous house.  But that's life.  I'm looking to replace it with 60"-65" plasma to cut that back but the CFO isn't convinced or at least I have not agreed to her terms. 
 
Enjoy.  Size does matter... for TVs.