Make the decision more business-like. The expected return on stocks is a little more than 1/CAPE + inflation, so 5% after 10 years. Increase to about 6%-7% if you are making regular contributions, decrease to 4% for withdrawals. Your mortgage is most likely the lower return option.
For home improvements, I recall the average US home is owned for 9 years (but you will know more about your plans). Any improvement will need to pay for itself before you sell. Basically even now I "expect" stocks to be competitive or better than most options listed here. I insulated my house in 2014 just after I found MMM, but I now admit that even assuming I donated my time for a good cause, the basic fiber glass insulation will not pay for itself in my timeframe, much less return 7% / year, far less match investing that money in an index fund in a tax sheltered account.
Honestly, the government should subsidize insulation down to just over the return of 30-year TIPS.