I had a DLP and I liked it, but I doubt I'd ever go back for various reasons. I actually never had a lamp go out (even though I bought a spare...go figure), but the entire "light cartridge" I think it was called did. Fortunately it was under warranty. Then the power supply went bad. Then, after the warranty was out it started randomly overheating and shutting down. To get anyone to look at that kind of stuff is just prohibitively expensive nowadays. I don't know what plasma/LCD repair is like yet, but I doubt they have to bring out several giant hunks of metal (light cartridge, power supply, etc.) to troubleshoot the problem.
Aside from that, from your setup there, you'd have to buy a different stand to make a DLP work in that space unless that one is significantly bigger than it appears in the picture. So that's another hundred bucks or more, depending upon how nice of a stand you want. It's also going to stick out into the room more due to the depth of the TV itself, although it does seem you have room for that. Anyone sitting on your couch won't have the greatest viewing angle either, but I don't know if that is a big concern for you.
If you can save up for a bigger plasma I would go that direction, honestly. Or make do with something a little smaller than 70 inches, which gets you up into much bigger dollar amounts. I know the math says bigger, but if you could make do with a 60" plasma you'd save a TON of money over a 70" anything. And it would probably be such an improvement over what you have that you'd be fine with the size. But only you can really decide that.