I don't mind paying for quality add-ons, although I hold payware to higher standards than freeway and don't feel the same gratitude as I do toward those great individuals who work solely for the benefit of the whole community.
Anyways, I have paid for all of the following and don't regret a single dollar (in fact, prorated over the hours I've flown, they add up to just a few cents per hour flight): FSNav, Activesky wxRE, FSD Gmax Cheyenne 400, FS Flightkeeper, Reality XP Garmin 530 GPS. The Cheyenne requires a high end machine (I didn't know this originally and had to upgrade the machine) and the Garmin is a resource hog too (but well worth it to upgrade your memory). I also have 2 SimFlyer airports near my home that I use home base.
Some time ago (FS 2000) I also owned Jeppeson SinCharts. I loved the program for planning approaches and being able to taxi around airports, but they did not have an upgrade path to FS 2002, so I haven't used it for a year or so (I could probably send it to someone if they're interested. I'm not using it. Is anyone still using 2000?) . I've toyed with buying the new version, but it is (overly) pricey and the Garmin does some of its functions.
As you can probably tell, I tend toward enhancing realism viz a/c flight dynamics and flight planning/navigation. Other folks prefer diversity in a/c or more eye candy scenery. All a matter of taste!