Yep, been there, done that - though not quite to your level
As an aside, I got both the Marlow and Lindrick RTW back in the day when there were deals to be had on them, and still both were a stretch for my wallet at the time. Those are two that I'm still very, very happy that I purchased; no regrets at all.
One tip that works for me is that when I find myself excited about a new find that I'm thinking about purchasing, I force myself to fence sit a reasonable amount of time to evaluate. Many times after a week or so of cooling off, I find I'm thankful that I didn't jump in. In retrospect, all of my worst mistake purchases were ones that I jumped on too quickly.
My last mental test is "what if it disappeared and wasn't available any more, would I regret not getting it?" - that's a great mental exercise for me; it really separates the wheat from the chaff. My Islays, which are from Purdey and on a different last, were exactly that situation since they discontinued them at the end of last season. I actually missed out until I was lucky enough for another buyer in my size for whom they didn't fit contacted me to sell.
All good points. I got into the shell game pretty late, after the Lindrick was discontinued and the prices of the Marlow skyrocketed. I still remember the most recent RL coupon fiasco (maybe two years ago?) where the Luxottica employee 40% off code leaked and worked on Marlows. I remember thinking "boy if I wanted to spend a ton of money on those shoes I would be pulling the trigger ASAP, but that's still too much." Then I probably went out and spent more than what they would've cost on 3 or 4 AE shoes I coveted less over a span of a few months.
I've wanted a pair of Marlows for a while, and the current favorable exchange rate caused me to jump in head first to the whisky GMTO, and to also jump on the Lindrick (which is discontinued, and cheaper than what it would be had it still remained in production by C&J/RL).
I agree that sitting on decisions is a great idea. Right now I'm thinking about how much I'd like to add a tan grain Pembroke, Islay, and chestnut Skye 3 to my arsenal. Oh and a dark brown grain Pembroke would be nice too.
It's so easy to get carried away. One thing at a time (or two, in the case of the GMTOs).