Question Is video rendering updated from VP 18?

Probably the biggest reason that I have used Vegas Pro in the past is that it had the ability to work with VASST Eventtools so that I could create really nice transitions between my 100+ clips, all at the click of one button. I currently have VP18 and wonder if VASST Eventtools is still a valid program that works with VP20?

That and has there been a significant upgrade (speed and quality) in the render software?  That's one of the reasons that I upgraded to VP18 was due to the vastly improved speed of rendering a project. 

I don't use VAAST tools, but their website reports they are compatible with all versions of VEGAS Pro, up to version 20.
I would send a message to them, if you have any concerns.

There is a HUGE list of New Features and Bug Fixes for VEGAS Pro 19 and VEGAS Pro 20.
Many "tweeks" have been added to the MAGIX AVC encode/decode (rendering) engine in VEGAS Pro, during the lifetime of VP19 and VP20.
There have been significant new features added to VEGAS Pro, since version 18 was released.
The developers of VEGAS Pro have been using a new approach for the last couple of years, where they add many new features to each version of Vegas Pro, during it's 12 month lifecycle, instead of adding all new stuff mainly at the beginning of each release cycle - this gives them more time to get things done properly, instead of rushing and ending up with new bugs to fix.

The No.1 improvement with the encode/decode engine is Stability and Compatibility with more formats.
Speed depends on what type of media you are working with and what type of computer hardware you have installed.