I'm no mind reader, but I've been married for 26 years now, so I have an inkling what this particular aspect is of your universe that makes it possible for you to make smaller purchases spread out over time, but not a single larger purchase (even if it would save money over all).

Here's a strategy. When you have enough money saved up for one of the smaller purchases, take it out in cash and stash it somewhere out of sight, out of mind. By the time you would have acquired all of the pieces individually this means you would have stashed enough cash that you could buy the whole gruppo at once, and probably have some left over. Since you now have a pile of cash, and it's probably most convenient to purchase using a credit card, just go buy one of those gift-card-like prepaid Visa cards and knock yourself out.

Or, if your LBS would sell you the gruppo at a price you would find acceptable, skip the prepaid VISA card and just buy from them with your cash hoard.

I've never used this strategy proactively, but check this out. If you buy something on Amazon and then return it, take the Amazon store credit option, and then don't use that for future purchases. I don't return things to Amazon very often, and then only if it's broken or the wrong item or whatever, but if I do return them I always take the store credit rather than have it go back on my debit card, because that money is now out of sight, out of mind, and that gives me flexibility to buy something larger from Amazon in the future and not have to explain myself to the family comptroller general.

Now I'm all for transparency and honesty in marriage, and I realize this makes me look like a sneaky villainous hypocrite. The way I sleep at night is to remind myself of all the times I didn't go out and get my hair, nails, fake eyelashes, etc. done.