I have no problem seeing that storage space or infrequent use can be an issue. I have never had any developer going bad, but I always make sure that there is no or very little air present in storage bottles. The exception is Rodinal which seems to last forever however bad you treat it. I'm in the lucky situation that I can buy Xtol locally for 24 USD at the current exchange rate. I expect that many of you pay less, but I can well afford both that and a fridge full of film. Others are not so lucky.
Regarding dilution I read an interesting article about Xtol in the German PhotoKlassik magazine some years ago. To get the best results you should not dilute Xtol more than 1+1 for T-grain films, but film with traditional grain will benefit from higher dilutions. I've followed that regime since and it seems to work very well.