I have the FZ38 and i struggled with the shutter lag between shots when snapping action stuff.
The EVF didn't seem really bad when looking live for me on that model but the black screen for a second or so after shutter release was very frustrating.
Saying that i did manage to get some good shots of some motocross events with it but gave up with burst shooting, its pretty useless IMHO.
I plunged for a S/H Nikon D90 in the end and i guess looking back that's what i should of done first time round.
The FZ38 is a great camera and takes great looking shots, i can't speak for any of the other FZ range. l'll keep mine as its very useful to chuck in the bag and its so light.
Anyway the viewfinder on any DLSR im sure will be a revelation for you compared to what experience you have had with your FZ30.
The only slight issue is the reduced view of the frame with the D90, its something like 95% of what you get. I've noticed it a few times but its not really a problem as you get used to it pretty quickly.
Looking back through the FZ38 EVF now is painful, its functional but its definitely a step backwards.
Buying lenses is the only other financial drawback, good fast glass doesn't come cheap and for good reason.
Just my very limited experience on the subject!!