IMO, good candidates for a RM are those that have insufficient cash flow to meet their income needs but have a lot of equity in their homes. It seems you have a good income and good equity (paying cash for the home) so a small first mortgage on the home is the reasonable route for some extra cash for upgrades instead of a RM, IMO.
My Mom was the perfect candidate for an RM. After Dad died she was left trying to make ends meet on SS alone which, after paying bills (insurance, util, food, etc.) she had a total of $9/day left over for any emergency or other expenses like eating out, car repairs, buying presents, traveling, etc. She owned the house mortgage free. She was talking about a RM so I made her one. I had $zzz/month sent from my acct to hers every month on the first and it made all the difference for her peace of mind and allowed her to have spending $$ for small 'luxuries'. The RM was drawn up by a lawyer and recorded. When she passed, we sold the house and the estate paid off my mtg. and the remaining balance was split between us three kids.
A RM can be a lifesaver for certain people but it doesn't seem that you fall into that category. Personally, I think you both should get some financial advice from a CPA and a lawyer and then make a decision.