What does a divorce atty cost? What are the annual costs of such a separation? Seriously -- not being a jerk here but seems you have a choice: be married to your current wife or be a market-driven property manager/owner. As others have noted, there is a third choice: give up the property mgr title. As that Brandon guy says now and again, you are either working for your business, or you are working ON your business. Smells like you are working for your business (with an admirable big heart, BTW). Gotta work the math -- and it isn't as cut/dry as some posters above suggest.
So that brings up: how much does a property manager take out of your hide? Because if you elect to go for 'market prices' on your own, your marriage will have that skeleton in the closet and a cascade effect on the mutual respect between you and the missus. Where does that end up over time, even if not in divorce court? If you decide to go for 'market prices' using a property manager so that the wife has less immediate knowledge of rent changes, you will spend the extra money or more gained from 'market rents' on property managers, but there may be other gains by using one (buffered from the other property mgr headaches). If the wife finds out, you still get to deal with THAT, but you avoid 3am water heater calls. Probably. However, it does let you work ON your business rather than FOR it, so stresses change and maybe even diminish. Unless you get a sucky property mgr or two.
Now that brings you full circle to doing what the wife suggests. Why not compromise with her -- work up a road map of rent increases that don't seem too onerous to her (or yourself), while bringing your assets more in line with your market over a set time? Here's where your 8th grade algebra comes into play. If you are under market at U %, and the market rates are increasing by M (in %/year as a decimal), and you want to be at market parity in (Y) years, you can figure your desired annual rate increase (R) using this formula: R=-1+(((100/U)^(1/Y))*(1+M)) I'll leave it to you to check the derivation from your starting point (A=P*((1+(r/n))^(t*n)) where t is in years, n is the compounding frequency in years, r is the rate, P is the initial and A is the final values. If your market is appreciating by 5% (0.05) per year, you are at 80% of market rate now, and you want to hike rates to get to parity in 6 years, plug and play tells you to raise rates 0.08978, or roughly 9%/year.
Just a thought for you and the missus.