The resale value of WRX/STi's is falling through the floor at the moment so now is a great time to pick up a decent STi for a good price.
The problem is you could easily sink $15k into a full conversion when you can probably pick up a Bug STi for around $16-18k in fair decent condition. Depends how attached you are to your current car I guess, but as a warning see Cat's build thread about how a strong attachment to a particular car can lead to massive problems (Admittedly hers was GC8 RX to STI).
Linky