The key is touch up paint. But matching existing paint is hard if not impossible. Assuming you still like the colors, just not the condition of existing paint, I'd make an effort to touch up before repainting. Previous owners should have left house exterior and interior paint with the house. Is it possible its stowed in your garage and you've forgotten about it? I feel your pain. I moved out of my last rental in part because there was not matching touch -up paint for all walls and I was unwilling to repaint the rental.
as I have already stated, it is near impossible to match paint. What you need are the remnants from the actual can or the exact specification of the paint. If it was a new home, I'd make an effort to contact the builders to get the specifications. If you had a way of contacting the previous owners, I'd say its worth a try to get a hold of the paint specification (that is its manufacturer, color number, and sheen). For lighter colors, especially whites, I have found if I have the exact spec, new batches match just fine. For darker colors, there are dye -lot variations (just like your chocolate chip cookies turn out different from batch to batch even though you use the same recipe) . That is, every batch can vary ever so slightly, which is why its imperative when the home is painted to purchase enough surplus for years worth of touch ups.
If you cannot get an exact match, there are a few tricks you can apply to eek out a few more years on existing paint. If you can get a close match, you can repaint your most scuffed walls and stop at edges and corners. You cannot detect minor color variations from one plane to another plane. So in other words, get a close match and just repaint the worst walls in their entirety, but not all walls. Hope that makes sense. When I was in design school taking color theory, my professor told us when he was a house painter, and ran out of a color, he'd simply have to paint one whole wall of the house in the slightly different tinted new batch because the light reflection and shadows on planes makes shade variations indiscernible.
Just to offer another opinion on paint sheen, my advice to anyone (I'm an ncidq certified interior designer), is to paint your gypsum board wall surfaces as flat as you are willing to maintain. Flat paint absorbs more light, making the colors appear richer. Kitchens, bathrooms, millwork are another story. I personally don't bother with magic erasers, or washing off finger prints. I simply go around touching up my walls every other month or so. I'm with you on this. Clean walls make a house.
In summary, if matching the paint for touch ups is not possible, then I would repaint and I'd make sure I never ran out of touch up paint.