Same setup here since 2017. Since then, RAM usage decreased by 60%. The admin panel is not something I'd need but it would be a nice-to-have. Started with postgres as I wouldn't go for anything else if I wanna use it for decades. It has 2.5GBs for 10users and I don't mind if it takes 10 or 20, that's something I expected. Never did a cleanup of anything, I just dumped the db and moved to OVH recently onto a new VPS with NVMe SSD, it flies.
The fact that I cannot delete attachments that users delete is certainly my biggest irritation, 50GBs of stuff I am not sure if I can or cannot delete, but considering the size, I am just gonna bite the bullet, couple terabytes should not be a problem in 25 years. But this is def something I would love to see addressed sooner rather than later. It must be a pain even for the matrix.org server team.
After moving to a better server I do not have issues with slow notification unless the phone is sleeping for longer period of time which is an android optimization (I'd assume). It is more reliable than teams at this point. One of my friends had issues but removing 15 old devices fixed the issue.
As for element-x, I did call out "the another rewrite" issue especially with android and I do think it makes things worse. I still do not know how am I supposed to fix calling and video between old and new clients. For now I don't bother with new clients and everyone is using old ones, but it starts to become an issue as classic clients are in maintenance only mode