Well, at the moment, although some of my original level packs have less than ten levels, the sum total is exactly 50 levels, so I've decided to re-jig the order and re-release the new versions as five packs of ten - which is nice and neat and makes me happy.
I've already thrown out one level that was one of my lamest ones, and replaced it with a "sequel" to another of the existing levels. I've also been play-testing them all to death and making sure they're not too boring to play. At the same time I haven't been worrying TOO much about backroutes - they can be irritating if they completely defeat a puzzle, but I'm all for alternate routes with skills left over and all that jazz is the player wants to find them.
The new packs, when I release them, will LOOK almost exactly the same as the old ones, but hopefully they'll play better, and that is the main difference I was wanting to make. I know I said I wouldn't be making any new levels from scratch, but if I decide that one of my levels is unforgiveably bad and can't be saved, I may just put in the effort.
I'm already more than half-way done, so I'm hoping to let my new babies out into the wild within the next week or so.
I've known right from the start that my humble efforts won't be reaching the dizzy heights of some the great levels on the archive, but as long as I've created the best levels I can personally make, I can sit back and relax and not be too bothered by any of their shortcomings. After all, I never even designed a level before about eighteen months ago.