I've always enjoyed pinball. No big regrets for me (from mid 70's to present).
Sometimes I may take a break from my pins, so I don't get burned out on pinball.
Besides, I have other interests such as: hiking, canoeing/kayaking, offshore fishing, watching movies and sports, visiting w/ friends/family, etc.
If price for a machine gets too high, then I just let someone else get it who wants it.
Are the 2 pins you are considering getting some of the ones listed on your wishlist?
What do you like about pinball? Playing pinball, cleaning them, buying parts, repairing, searching for next pin(s) to buy, buying/selling/trading, owning pins, and/or having friends & family over to visit & play pinball? Is the artwork and/or theme of a pin important to you, or just the gameplay?
Going from 2 to 4 pins in your collection seems ok to me, especially if you think you will enjoy these two new pins. Buy pins you will enjoy, not some unpopular pins w/ crappy game play or poor artwork, or in too horrible of condition to enjoy.
And ....w/ 3 or more pins you can have a pinball party!
Do you know anyone that lives somewhat local to help you make repairs to your pins for some of the more difficult issues/problems.
I see that you are in St. Louis, MO area. That is a good city to live in concerning pinball. Good central U.S. location, some good places to play pinball around town.
Not sure what your concerns are, or why you are hesitant to buys more pins.
It sounds like $ and space for your pins is not the issue.
Do you have (or will you have) some free time to spend on your pinball hobby/collection?
If you plan to travel and pick up machines yourself, then you probably want to buy pins within a 300 mile range or closer, so you don't have regrets over time & gas money spent picking them up.
You can always sell one or more of your pins, if you feel like things are getting a bit excessive.
Nothing wrong w/ selling a pin imho. It justs lets others also enjoy owning a pinball machine.
At least w/ pinball machines you physically get something for your money. You could spend thousands going to sporting events/concerts/plays, or on airfare/gas for vacations/cruises to distant locations, etc.
Let us know when you get some more pins added to your collection.