I have two rules to guide me that can be summed up to maximizing the joy of spending: It's not what you have, it's what you do with what you have that matters. Going with a car example, spending significant income for a nice car that you use for normal transportation like commuting and shopping will bring little joy. On the other hand if you are into motor sports, regularly tour on or off-road, like to restore classi…
This is a really important idea to me, it's a way of optimising your spending without doing big central planning. If I would get more from doing X rather than Y, why would I do Y at all? You could then repeat that with 10 trips abroad vs some other thing.
You can also compare a relative thing as well. You may need a new car, but can choose between different options. If one is £5000 cheaper than the other - what's the most fun you can possibly have with £5000? Would you rather whatever that list is for you or the more expensive car?
Would you rather have a larger rented apartment or £Z to spend at restaurants every month? Or £Z on track days, or whisky, or having an extra few days off a month?
All of these things can be answered any way and it's totally fine - the key is to identify what provides the most value to you without getting stuck in trying to optimise your entire life as that's (to me) paralysing.