SuperfuzzSomeone got their hands on the paid mods from the workshop and did a quality test run through. They found that with the exception of one of the armor mods (Gifts of Akatosh), they were all pretty shit quality. Bad clipping with models, only a male version and no female version, completely OP and gamebreaking stats, not even implemented in the game properly (either have to get it through cheats, or else it's placed in some dumb spot in the world where you don't even have to find it, i.e. leaning against the wall in the starter town). The location mod included boring cut and paste textures (they used the dirt texture for the ground as the ceiling texture too), absolutely no voice acting for any of the people in the town (barely any vanilla lines even added, you basically can't interact with any of the people), and just overall shitty quality. Not to mention some of these mods add clipping and bugged textures to vanilla stuff in the game (somehow).
That's what the paid workshop represents right now. Shittily and hastily thrown together mods with pretty screenshots, designed to make a quick buck. Sure, this might change over time, but I'd expect a VAST majority of the paid mod market to be saturated with these shitty quick buck mods.
The other major problem I forsee in the long run, is when a new game like Fallout 4 or Elder Scrolls VI comes out. When the modders get ahold of the new modding tools, there has always been a period of exploration where they learn how to use it, tweak it, bend it, and get incredibly creative with it. Part of this exploration is sharing what they discover and learn with the rest of the modding community, and this always results in incredibly high quality and fantastic mods for the game that extend its life for years (see: Skyrim, Skyblivion, Skywind). But if mods are monetized, these modders aren't going to share what they discover with people because they want to have the exclusive mod that they can sell for the big bucks. This lack of sharing is going to result in overall lower mod quality, and less enjoyment for all of us nerd gamers.
I think you nailed it holy shit