Ive driven both. Both are awesome. Speed3 happens to be way more awesome then the protege. But the protege can still hang and it handles Very good. Ive talked to many customers here that have traded up from a speed protege to an rx8 or speed3 and miss the protege.
I assume you are talking about a protege though because there is no 03 speed3. And speed 3's DO come with 18's from the factory.
as for 50k+ for close to ten grand i dont know. Your risking it. Really take a close look at how it was cared for. It is a performance car and someone has probably done a lot of "performance" driving in it. etc. etc.
The proteges really dont have many problems. Pretty much just the valve cover gasket usually always need to be replaced and sometimes the air intake hoses can get brittle and break and you get a code.
The speed protege stock turbo wastegate actuator also fails fairly regularly and while labor is not that bad the actuator cost is. Youd probably be better off with a new turbo. Other then that you can rag the crap outta them and they will take it. Hope i cleared some stuff up.