Ouch!
A friend and I almost made the same mistake by buying a set up like that. We had already signed at a quilt show, when later on in the day some one educated us about throat space, but the lady let us out.

Various Triangle rulers. Whenever I didn't get my HSTs finishing the rigth size I'd try a different ruler to cut the triangles. NOW I know the problem always was my 1/4 seam allowance and not the cutting. Well, now if I get bored with one I can use another. I get my seam allowances accurate nowadays.

Thanks to every one here on QB I have not wasted my money on fancy rulers and quite a few other tools and notions. My favorite rulers are from my own tool bag from the good old days of pre-retirement

I have too many to tell. Some have never been opened.

I can't think of anything right now I thing I will never regret is buying is my two 9" throat machines. I use them all the time and can quilt any size quilt I need to on them.

Last year my DH gave me EQ7 for Christmas, and I feel so guilty that I have only used it a few times - mostly just playing around. I haven't disciplined myself to sit down and spend some quality learning time with the program.

It really does happen to all of us - many of the rulers I have I did get when a lady left them at the rec center where my husband worked, she didn't want them anymore and the LQS wouldn't take them. But then a few rulers were bought when they were on sale at quilt shows and before I buy another one I check to see if I already have it. And I also share, when someone wants to try something, I figure if they like mine, then they can buy it. If it turns out to be more trouble than it is worth they know without the investment.

My little clover iron is one such tool - when I saw it demonstrated it looked like the best thing since the sewing machine. But it was just not the way the it was for the demonstrator.

Also, many people never make the same pattern twice, so if I have to tool and they will only need it for one quilt, why not use mine and save a few dollars?

I have bought entirely too many books.

I once won $200 in a contest & used it to buy a Martelli cutting board & cutter. Both were big mistakes. Didn't like the cutter so gave it away. Use the cutting board under my Olfa mat bec it is slightly larger & the numbers show better when I'm cutting yardage.