Sherry has many characteristics in common with port. However, sherry has none of port's fru-fru-ness. Let's face it, sherry has a poor reputation. This is a shame. I've enjoyed what sherry that I've tried. As longs as you don't buy the sub $6 range (been there, done that), you should be gold.
I haven't tried a marsala yet. Most internet references pull up recipies when you enter marsala. It's used in much Italian cooking.
I'm discovering a bit about wine culture, too. On one hand, there are the few and far-between practical sites with the attitude, "it's all about the enjoyment." On the other hand, many sites and all wine sellers demonstrate that it's about wealth, status, and cultural awareness. Mostly, I've learned that "sweet" or "dessert" wines are low on the wine snob's radar. They just don't get the same respect.