I think you have to ask yourself why you want to upgrade first of all. What is it about the sound or experience that you want to tackle. Think about what you are hearing.
typically I’d say in any setup upgrade speakers first. they will be key to the character of you system, then you can tackle amp and sources.
if you’ve already done this and decided turntable is the weak spot, well I’d consider carefully the budget here since you need to factor in a decent cartridge/stylus. at budget of £500 would you therefore really get a significantly better turntable?
there are certainly things you can do to improve the debut iii itself also. I have been using one for many years and am still quite happy with it, but I’ve probably spent more in upgrades than the TT originally cost me. This may sound daft because the total likely would have got me a better turntable, but it’s been easier to manage the outlay a little at a time.I perhaps do want to tackle my turntable as next/final upgrade, but will wait until I can make a much more significant step up, maybe a project x8 or something in that bracket.
Considering upgrade to the debut, if you are still running the stock cart I’d suggest you definitely tackle that and that does not necessarily need to be an expensive purchase to get a big improvement. I have a denon dL-110 cart which I love, but I bought it at a time they were not so expensive, and it did mean I had to replace the platter to an acrylic one. I am sure a quick search here will reveal many cart suggestions.
The other things I’ve upgraded…., replaced with s/e motor kit to reduce hum and for more speed stability, added aluminium sub platter, sorbothane isolation feet under the stock ones, and a project speed box s2 introduced.
you kind of wonder if I might get into the realms of the laws of diminishing returns, but I feel like each thing I have done has in and of itself been worthwhile.
my more recent upgrade (a considerable one), the amp, sorted out another weak point in the process that being my phono preamp, which previously was a CA 540p. Actually when I started down the upgrade path the first thing I did was to put in the 540p which I got second hand for maybe 40 quid or something, because I had a really nasty thing from maplin prior to that!
so I guess what I am saying, unless the TT is completely knakcered maybe at least get a new cart and breathe a little more life into the debut iii…. if you’d “go with Betty but still be thinking of Wilma” (red dwarf quote) then perhaps the small incremental steps in upgrades won’t satisfy