I feel like an Annual Pass is 'worth it' for a frequent park visitor, solo or not.
But I've also never done the parks solo, so I could be way off the mark.
The short answer:
You should get the AP which best fits with your personal preferences, budget, and future travel plans.
The TMI answer:
My husband and I recently decided that the 'Magic Flex' APs would be a good way to test the passholder waters.
In addition to park entry, the 'Magic Flex' option offers the benefits we're most interested in (free parking and on-site hotel discount), with
blackout dates that fall during times we aren't planning to travel, for what we find to be a reasonable price.
But that's just us! If you're looking for maximum 'bang for your buck' / the full VIP situation / something else entirely, you may be looking to purchase a different AP than we did.
You can find more detailed information about each Passport on the
official Disneyland Paris website; here's
a link to the PDF they provide, which compares all four options side-by-side.
This seems tough-to-impossible to answer, but I'll give it my best objective(ish?) go:
The cost of a single-day ticket for both parks is approx. £60 (info found
here).
You could convert the cost of whichever AP you're interested into GBP and divide that by £60 to get a rough idea of how many park days = face value of your chosen AP.
For example: I paid €189 (or approx. £165) for my individual 'Magic Flex' AP; £165 divided by £60 = 2.75.
So, my AP cost less than 3 single-day tickets, but it's good for park entry on 300 days of the year.
That feels 'worth it' to me, but everybody's 'worth it' is different.
Rather than going by my oversimplified calculations, think about your own plans to visit
Disneyland Paris over the next year; look at the cost of the relevant park tickets (from Disney and/or wherever else you might purchase tickets) and compare that against AP prices & info to help determine how many visits / what length of stay would make purchasing an AP 'worth it' to you.
If your desired travel dates happen to line up with any special offers or holiday packages, you might also want to compare the associated discounts/benefits against the benefits of whichever AP you're thinking of purchasing.
Hope this ridiculous novel-length comment hasn't made things even more confusing. Good luck with your trip planning/AP research!