While I more or less rejected from the outset the idea of learning tunes solely out of professional obligation, I sense something of an impasse setting in over the last several years that makes me a bit uncomfortable. When someone calls an old standard I don't know, I still go home and look it up; the problem is that whereas I often used to be impressed enough to want to learn it, I now find myself gagging virtually every time. I don't know that many tunes, but it seems increasingly as if I know most of the ones that I care to know; such it is that the "obscure standard" remains a beguiling oxymoron.
There's so little to recommend tunes like Summer Night, I'm Old Fashioned, and the like. Even in an era of unprecedented narcissistic aping of classic jazz, they don't seem particularly necessary or even useful as foils to business as usual, at least not based solely on their relative obscurity. I would also argue that it is these tunes' very lack of "interesting" harmonic content in their original versions which seems to beget irreconcilable regional variations that can frustrate the prospective student: as best I can tell, Summer Night, for example, seems to exist in two versions, one of which goes to IV in the 7th bar, the other of which merely works its way back to I. That's not "substitution" at work so much as underdetermination, no?
To my ears, the various ways of playing the 10th bar of Alone Together are more symptomatic of inspiration, of attractive possibilities which both work well enough to capture the imaginations of the jazz community, and whose relative merits most of us wouldn't think to bicker over even if we'd agree that it's better to pick one explicitly before attempting a performance with people we don't usually play with. This variation in Summer Night, on the other hand, just sounds like a mistake, and at that, a mistake of the type that competent musicians simply don't make or accept whether they're an established band or a jam session punching bag.
It is well established that master improvisors in musical traditions the world over tend to exert their mastery over what in the jazz tradition would be considered a scandalously small repertoire of distinct pieces or forms. The lesson for modern day jazz players? Knowing 1,500 standards was a commercial venture from the start! Occasionally, it may be a voyeuristic one for the real zealots among us; but was it ever truly an artistic one? Indeed, could it ever be? Some would ask whether learning tunes is not one of the best ways for improvising instrumentalists to build vocabulary. Not necessarily, I would say, if the tunes in question are "singer tunes," i.e. "pop songs," i.e. vessels for the unencumbered delivery of lyrics in service to which the melodic and harmonic accoutrements have been purposefully pared to an unobtrusive minimum (so much so, in fact, that the recorded legacy of these tunes betrays literal ambivalence towards them as musical structures). If you play jazz in 2012, I think you have to face these questions eventually, and also realize that you can't trust anyone who writes for the International Musician or publishes jazz education materials to answer them for you. In any case, it seems to me that the road to encyclopedic knowledge of standards has become littered with half-remembered versions of unmemorable tunes, which is one of the best reasons I can think of to permit oneself to specialize just a bit.