It all depends on what your requirements are. We all differ in how much deviation we accept in our negatives. Some find it perfectly fine as long as their negatives scan OK and they can get reasonable colors out of it with some post processing. Others feel their process is only under control if density measurements on test strips remain within the boundaries set by e.g. Kodak.
In general, kits like the X-Press kit, Jobo, Rollei etc. are not intended to be replenished; there's simply no replenisher marketed for these kits. You may be able to replenish the used kit with replenisher oriented at minilabs, but if you're going to use minilab chemistry anyway, I wouldn't bother with the amateur-oriented kit in the first place.
Re-use of developer will
always result in density shifts from one batch of film processed to the next. Whether this is within acceptable boundaries is up to you to decide; see initial remark above.
Re-use of bleach and fix is possible to an extent since both processes should go to completion. Both bleaching and fixing can be done again if they turn out to have been incomplete/inadequate.
cartridge chemicals for V30
Cartridge chemicals are generally not quite as attractively priced as regular minilab chemistry that's not associated with a particular machine type. It may still be (much) cheaper on a price-per-liter basis than e.g. X-Press.