Jras -- I share your concern. Unfortunately, the current FCC spacing standards don't account for the interests of DX hobbyists (or, indeed, for the needs of rural residents who might depend on moderate- to deep-fringe reception of certain signals.)
The FCC will license a new signal on a given frequency as long as the new signal's 40 dBu "interfering contour" (around 35 dBu actual strength) doesn't touch the existing signal's 60 dBu service area. Sounds OK in theory... 25 dB may sound like a lot of headroom. However, in practice, it's not. FM receivers exhibit the "capture effect" of selecting the strongest signal on a given frequency, rejecting the weaker one entirely... but this effect requires a difference of around 4 or 5 dB in order to provide a completely steady signal as you drive along (or move the antenna in your house.) This, of course, occurs on both sides of the "equal" point... the result being that anytime one puts a new station on an occupied frequency, there will be a slice of the map where the frequency sounds like useless alternating crap.
Depending on just how close the new transmitter is to the 60-service of the existing station, this crescent could run through portions of the existing signal's 47 dBu or 50 dBu or even, in some extreme cases, 55 dBu service area. This is partially because a low-powered signal (such as a translator) "drops off" so quickly as you move away from it. Working this in reverse, as you move closer to the low-powered signal, its strength INcreases a lot more quickly than the other station's strength DEcreases. As a result, the impacted area of the existing station's coverage occurs closer to the existing station's 60-service than one might otherwise expect.
There's a particularly egregious example of the above going on in my home market as we speak -- Clear Channel has applied for a supposed "fill-in" translator, here in oh-so-mountainous Minnesota, for 100.3 KTLK. Problem is... this translator will be located in an eastern suburb which KTLK serves with a signal of over 75 dBu. It also just happens to be located right on 96.3, the frequency of KTTB (B96)... a west metro rimshot Urban, with some signal problems in the eastern suburbs, that competes with Clear Channel's KDWB. CC's engineers chose a site that sits right ON B96's 58 dBu, then -- in order to clear spacing requirements -- made the translator so directional that its coverage basically looks like a giant pickle pointing southeast. (The back of its pattern clears its spacing requirement by around 150 feet.)
Anyway, in summary, a 48 or 50 dBu signal might not sound like much these days, since they aren't making receivers like they used to -- some Walkman receivers and clock radios have trouble even with signals in the low 60s. But it's really not that difficult to catch in a car, or even with a decent home receiver and a simple wire... and as mentioned before, some people in rural areas prefer or even depend on certain stations whose signals are somewhat "fringe"... so I, for one, think the FCC ought to reconsider its spacing guidelines.