The Mage's Guild are worthwhile if you want to level that skill line to 10 and get Meteor (a great unti) and all passives.

There are dailies in most of the DLC zones, too. Western Skyrim, both Elswyers, Murkmire, and Vvardenfell all come to mind. Mostly delve missions, WB missions, and bounty/fetch missions.

I generally do two daily delves a day in two differing zones based upon completing the motif drops for that particular zone's dailies. As I complete the motif, the two zones I do evolve to other zones. Currently doing a daily delve in the Reach and another in Summerset. Over the last few months I've completed the daily delve motifs for N and S Elsweyr and Western Skyrim. I long ago completed daily delve motifs for the Undaunted and several other zones. A review of your incompleted DLC and crafting achievements can help reveal which motifs you've already completed or how many pieces you have remaining to complete. Due to diminishing returns once nearly completed with a motif, I generally buy the last one or two missing pieces from the guild traders.

You actually really want to be doing those daily crafting writs. Great source of xp, gold and mats (gold mats sometimes, too) and they only take about 3 minutes to do if you're on PC (there's an addon on PC, Lazy Writ Crafter, that will basically do the job for you). The recipes needed for proviosioning ones are green recipes that I believe are sold by NPCs chefs (even if not, their market price is probably about 100 gold) so acquiring them shouldn't be an issue. You can also craft like 200 of the food/drink required and then just carry them around and give in 1 per day (works great with Alchemy writs too).

That aside, there's actually a pretty standard pattern in the last few years: every new zone has 3 dailies - delve, WB and zone theme specific-event (Geysers in Summerset, dragons in both Elsweyrs, Harrowstorms in Western Skyrim and Reach). They can usually drop either motifs or furnishing plans, and the zone events also have a chance of dropping something of the sort (albeit low). The newer the dlc, the pricier those motifs/plans usually are as not too many people have acquired them yet.

Far as 'solo' part goes - you can easily solo the delve (altho personally I find these dailies boring), soloing WB will take some effort and soloing the zone events is nigh impossible (at least dragons and HS. Geysers are pretty easy to solo imo, on the level of your average WB). However, there're usually people farming this stuff all the time, especially in newer zones such as Reach right now. Some old ones are not too bad too - for example, good old Wrothgar dailies are as live as ever now since Briarheart set from there goes for a lot of gold so people are killing WBs almost non-stop there. You'll often see people calling for help with WB and such and offering to share the daily quest in return in the zones that people are farming. If you don't wanna group, Reach is probably your best bet as there'll probably be people killing things wherever you go.

A lot of the daily quests give you rewards when you do enough either in furniture (eg the waterfall in summerset), or titles (clanfriend etc). Thus I tend to run different ones at different times until I get what I need. Others are useful to run regularly because they give crafting motifs and/or materials - eg the elsweyr ones for shimmering sand.

Clockwork city has some nice fun ones, and the gol coast ones like the Kvatch arena quest is always a bit of fun.