A typical rental investor should be looking at a perspective property from a point of return on investment, ease of ability to rent, ease of ability to make repairs (and there will be repairs), and many other factors. You can read the article I wrote on my blog about purchasing rental property in the link below.
A typical retiree purchase typically involves downsizing, yes. But it also should include questions about maintenance. But these questions many times are different maintenance issues than rental property. For example, a rental property may be interested in ease of access and replacing components as cheap as possible. This may not provide the best looking option. Whereas a retiree maintenance issue may deal with things like home exterior maintenance and having exterior siding that does not require paint every few years to maintain its look.
I am still bullish on the real-estate market in the long haul. So I do think you can purchase a property today for less than you will be in a few years. But this is probably not a good reason to try and combine the two strategies.
People's plans change all the time. They decide they want to live somewhere else. Or one of the folks dies. Or one becomes ill and they want/need to move closer to relatives. Or maybe the neighborhood changes. A neighborhood that looks great now may not be so great in 15-25 years. Or the rental property itself may be pretty nice now, but kind of dated in 25 years. Or maybe you want everything on a single level, but you've bought a multi-story property.
So: Buy a rental property strictly as a rental property. OK, it can be in the area you'd like to move to when you retire. And maybe it can be the same sort of configuration (townhouse, single-family home, etc.). But make sure that it works, today, as a rental. Then, in 15-25 years (or whatever the time span is), if you still want to move there and everything else still is OK, then do so and enjoy. But base your decisions today on it being a rental and only a rental.
Hope that helps.
Take care and good luck!
Are you absolutely sure that the rental property is where you would want to live when you retire? Rentals are generally different than owner occupied properties, so you may want to rethink it. By the time you want to live there, you may need to put a lot of money in to upgrade it.
I've thought of doing the same thing myself, so it isn't a crazy idea. It may be worth it if you get the right location because it is all about location.