Grouch, have you ridden a TTR to know its inferior?? Horses for courses, a WR450 is a cracking bike, for a days trail riding on proper trails or a days enduro racing/practice, much like a KTM300exc.
The 450 isnt as lairy as its 426 predecessor, but is still a potent bike(more useable power, better spread). The service intervals and costs on these highly strung 4 stroke race bikes (because that is what they are) is a lot more than your common or garden 125, and more than the TTR or XT.
What do you plan to ride most? Would a supermoto be a better bet?
Dont discount the suzuki DRZ, they are more powerful than a 250, more reliable than a WR450, cheaper to run, and whilst being more novice friendly, I dont think you'll get bored as quick as you think.
Ive have a TTR 250, which is great for a days trail riding, but is uninspiring on the road, my Dad has a DRZ 400, and it is as comfortable on the road as ikt is off, and its amazing the stuff he can do on it. A KTM 300exc would be a good bet if you really want a silly quick, featherlight, chuckable, fun machine. I was fortunate to swap my DT175 for a bit as a mate with the KTM fancied a go on it, like alot of things everyone should try it at least once!
Having said all that, even the WR250 should be given a look, a few I know have started trail riding on them, and experienced riders love them too.
Whatever you buy, if you buy sensibly you will always sell it on for what you paid, or possibly more. Buy something, try it, and sell it if you dont like it.
I would see if anyone you know would let you have a go.