It would be nice to have PT on steam, but there would have to be an overhaul to improve the interface and allow compatibility.
Also, the maturity of the steam community is pretty high for the most part, meaning many of the superfluous threads and spam comments could not happen, else PT would be frowned upon.
Every bug needs to be fixed, server errors need to stop, improved search system to get rid of spam saves, login needs to be improved, mod installation would need to be more user friendly.
Sounds like most of the things you mentioned are fairly easy fixes. The bugs could take a little longer, there is a way to fix those though too. What TPT would need is some testers to pretty much test every scenario with every particle in there. Another thing would be making the game speed a little faster.