I remember reading an article about a guy who had no layout, but in anticipation of having one ,bought buildings, kits, rolling stock and engines, lots of everything! For over 10 years he did this, with everything still in boxes! Finally the time came to finally have a layout! Every weekend he and his friends opened boxes, it was like Christmas every weekend, stuff he had forgotten about suddenly was there and he had a use for it! A great deal of fun discovering things and finally using them the way he pictured them over the years! I am in that situation and look forward to weekend Christmas openings some day soon! Though I 've slowed down on buying, I still go to York, with a vision in my head! I follow this forum with an eye to using what I learn here some day! Silly, maybe, but better to have a dream than not!
I am in a similar situation. Gave up my last layout in 1972 for the usual reasons, but fiddled with HO in the meanwhile. In 2009 I started to design and collect stuff to build my layout after my 2014 retirement. Finally started to open boxes and put it together about 3 months ago. As mentioned, it is like Christmas 1957 everytime I work on it!
I will say, though, that I had a plan and a design, so I only overbought by perhaps 20%, with the exception of PW transformers, which I discovered I don't need at all, and rolling stock, which I perhaps have twice what I need. But, judging by what others have aid, perhaps twice what I need is really not enough....
I guess my biggest regret was buying any PW. Barring the sentimental attachment I have to a few pieces, I am generally disappointed with it. In 1962 it's all we had, but I will take modern any day.
Going forward, we will clean out the items that are not part of the plan, and make changes on an "exchange" basis only. As others have also mentioned, I feel that too much stuff weighs you down. YMMV