This used to be a bigger deal than it's going to be in the future, and on the other hand it's not absoultely clear if this will always remain a beenefit of lowest-rung status.

It used to be that the only seats with legroom like exit row seats were actual exit row seats (and then only some of them on some planes!), and you couldn't buy them ahead of time no matter how much money you had.

But now the trend is to put a bigger legroom section on the plane (E+ on UA, which had it all in place until it merged with CO and now has to get back to having it all in place again, EC on DL, and the upcoming MCE on AA). And the whole reason those are becoming popular with airlines is because they've realized they can sell those seats as an added cost option.

So while in the past elite status was the only way to get into exit rows, in the future incremental money will get you into E+/EC/MCE even without status (at least on mainline planes, and with some airlines even on many RJs).

(Though status will lower the cost and ease of getting into E+/EC/MCE, it will do it for only one of the majors, while incremental money will work on more than one.)

Now, incremental money is a cost, of course, but it has to be compared with the cost of getting to MM status (if your "natural" flying does not get you there "automatically").