Used CRF issues need opinions

I got a used (04 crf 450) Was told that I needed to replace the valves, and Piston wile I was at it. Well I ordered kibble white valves springs etc. and a wesco Piston kit. After further inspection this bike was poorly maintained. the sub frame bolt that holds to the frame under the seat broke in half. That concerns me bc if I was riding it when it happened It would have really sucked. I looked ar the air filter and there was not even any oil on it and it had a small hole in it to boot. My question is Is this even worth fixing? Will the new top end and some maintenance get me back on track is is it most likely a POS? Will the bottom end fail soon from the lack of maintenance?
Thanks for the help guys

By the way I payed about 1900 for it and have about 700 in parts to put in. My thinking was that 2600 was a good deal and even with 500 more I was still doing okay for a 450.