Congratulations! You do have a dilemma, don't you? Hard choice, indeed.
This past week, my boyfriend read me an article from the Philadelphia Enquirer, (their daily paper) regarding sommeliers in that city. Apparently, there are only 6 in the entire city. On average, they work 70 hour work weeks, earning approximately $50k.
Granted, Philly is not the wine capital of the world, but it is a city, nevertheless, and the pay scale is probably only slightly less than another major city. There are restaurants of quality in Philly, like Le Bec Fin.
Anyway, my point is, if this is a dream, go for it now before it's too late and you miss this opportunity. It's hard to make no money for three months, though. I'm sure you've considered your options, financially, so I won't ask about that. The last thing I want to say, regarding the letter, is that it sounds, to me, like they are looking for a 'just about to graduate' person to do quite a bit of grunt work. I expect you've done your share of grunt work already, yes?
I've always pictured the sommeliers as ethereal types of people who can tell you more about a grape than the vines, themselves. I see it as a well earned title of respect and education.
How do you feel about the title you've already earned? Would you consider trading it for another? I'd love to know which way you are leaning. And, good luck.