Oh, I don't think you really NEED to remaster the old games (old... your first game is from a year ago...) unless you really want to. I know how you feel but I know lots of writers who fall into the trap of remastering old stuff with their new knowledge and kinda get trapped in a loophole of always wanting to get everything to their current level xD BUT YOU WILL ALWAYS GET BETTER! If anything I would just remake a few sprites with your current art style. Maybe for a bundle of all three games when the third one is done...?
The ATL effects will have an influence on the browser version but imo the worst offender for causing lag in the web build are the transitions. I am not sure if using ATL (changing alpha of an image) or using the pre-made renpy 'dissolve' statement would cause more lag. I don't think changing the position/rotation/zoom/etc of a preloaded character sprite should be that bad. What to avoid when creating a game for browser is something I am aiming to explore myself bc a lot of Renpy users are struggling with getting their game optimised for the web build. Your games aren't that big (I think the download for your latest one was around 130mb, MBM was even smaller) so you aren't doing anything wrong regarding your file sizes either. I think it's a 'renpy issue' and I wish they would create a better guide on how to optimise games for web. I hope that when/if they add the web build option for renpy 8.0 that it will be better since they usually add bug fixes/improvements with each version.
Ultimately, I think if people like your game they will also download it ^^ But you cant really know unless you tried. So maybe uploading just the first 10 minutes for browser and locking the rest behind the download could work. Sort of like a 'short demo', so that people can peak into the game. (As an example I would lock the browser version for ETPG at the point where Fritz lands on the house. That should make the game small enough to run in browser without lag and long enough for players to want to find out what happens next)