Pat,
I'll be honest 4 strokes scare the crap out of me, the performance is unparrelled, but the thought of blowing one up has me spending money on pm stuff just to ensure they don't give me trouble. when we raced 250f's we got a new one every year and as such had no troubles, we still get a new 450 every year or two, and then I've got a couple that are modded for a specific competition, those get new cranks every other year and new valves and springs every year. I would check the valves to see if their loose in the guides and not replace them if they don't need it, as changing them is somewhat of a challenge if you don't have the proper tools. So to answer your question on valves, the reason they go titanium is that they are so light and have a minimal performance edge over stainless, I think stainless are more durable, but I don't know this from personal experience, even though for a play bike I wouldn't have any qualms about trying them. Not sure how compression would show good on the leak down and the valves still leak, I'm only telling you what my experience is. look at heavier valve springs, there has been some debat as to whether this is the reason the valves fail or at least a contributor, once they float they beat the seats out and then they are on a road to complete failure.
The 04's as I recall were a bit harder to start anyway, pro circuit made a shorter kicker, allowing the motor to spin faster and theoretically start easier.
