I'd still say it's worth it, even though the quality has dropped in recent months.
Subs can be had for £30-35 a year, say £2.50/3 a month, for which you a handful of games on all formats and, if you've been subscribed for a couple of years, a decent back catalogue too.
The average quality of the releases has slipped, but the last twelve months have comfortably provided enough games to convince me to renew again (Resogun, Velocity, Fez, Guacamelee and Sly 4 to name a few). If you have a proper gaming PC or only own a PS3 and have no intention of upgrading to a PS4 down the line, then it's probably worth considering letting it lapse, but I'd still renew now.
I'd like to see the PS3 getting two AAA titles a month again, as the last few months have had a really poor selection. It's a shame, as I have no intention of unplugging it for a couple of good while yet. Persona 5 next year could be a great swansong and the console is still a lot better than the PS4 as a media player. That being said, the games are drying up on it and a lot of recent releases (unsurprisingly) really struggle on the hardware, so I don't really mind the increased focus on the Vita and PS4.
PS+ works particularly well for the Vita: buy the odd retail title to complement those that you get in addition to a steady stream of good indie titles, which suit the handheld really well. More and more games have cross-buy as well, so the vita regularly gets three or four new titles a month.
A lot of the PS4 titles have been poor or forgettable, but there have been a few gems too.
Edit- As DD suggested, I'd love to see a collection of PS3 classics on the service: one new AAA title and an older one would be brilliant.