The carb can be fixed for under $10.
For street use, a sprocket change is under $20.
Switch to an ester-based synthetic oil and the trans will shift easily.
You call it crude, I would expect a poet to recognize elegant simplicity.
If the TW had 250 cc, fuel injection, a six speed transmission and liquid cooling, it still wouldn't be a KLR 250. It would be a much better motorcycle than said KLR.