Your room is 10% longer than it is wide. Until someone corrects me, I'll claim that it's not really going to be a problem. I think 5% is the boundary you don't want to flirt with.
I can't answer with certainty whether a few DIY (or store-bought for that matter) panels will make a big improvment in your room. But it's probably safe to say they will add some benefit. The windows, hardwood floors, and wood paneling are all very reflective surfaces for higher frequencies, so I'd imagine your HT has a bit too much reverberation going on. Do you get listening-fatigue while watching movies or listening to music? Is dialog in movies hard to make out clearly? If not -- i.e., if you're already happy with the way it sounds -- then you don't need to do anything, right?
I'm trying to tame the reverberations in my basement HT, and I've gotten several suggestions so far. I've put down an area rug, I'm building some DIY panels for 1st reflection points, and I might build curtains to make the room more rectangular. I've also heard that bookshelves with books or other odd-shaped items can help diffuse the sound. Are your wood panel walls bare at the moment? I would think that substantial book-shelving or DIY panels would probably help. Do your windows have fabric treatments? Short of opening the window, adding thick curtains is about all you can do there. Can you add an attractive, not-overbearing area rug between the seating position and the screen?
Good luck!
