I'd say the Diamond Home is the most worthwhile purchase in the shop, by far. However, it's quite pricey, and the road to get the 150.000 dcd isn't easy. I'd recommend buying the Gold Home (5 sethomes) as a sort of stepping stone towards the end goal.
Beyond that, I'd say going for one of the Shop deals is a good idea, either Iron or Gold, depending on how large you plan on making your shop. In my experience, Diamond Shop is not quite necessary for the majority of players.
I'd also recommend getting yourself the end warp card (but not the Lesser variant), but I'd craft this instead of buying it for a large amount of dcd (see also Minecraft > Vanilla > Custom Items).
Other options in the shop like claimblocks or spawn eggs are good to have at times, but entirely depending on your needs. You acquire claimblocks through playing as well (100/hour), and I personally never had to buy more.
Aesthetic options such as Gadgets, Trails, Particles and NPC's are the purchases you could make 'just to have them', after getting the things you've been truly after.
I'm saving for the diamond home. Just 461139 dcd to go...
Edit: it's less now.
The Diamond Home costs 150k dcd. With your current balance of just under 40k, you'd "only" need 110k dcd, not 461k