Is it worth upgrading to SSD or just to buy new? I'm deciding whether or not to upgrade to SSD's in my Late 2011 15" MacBook Pro 2.4 GHz i7, or if its finally starting to come to that time where I need to just fork out and buy a new MacBook.

I'm not sure whether upgrading to SSD will solve my problems for long, as my laptop is taking around 20 - 30 minutes from a cold start to just open applications... I have tried everything, even a complete wipe of the HHD and a fresh install of the OS.

Thoughts?
I have a Late 2011 MacBook Pro too. After upgrading to Yosemite last year, I was thinking on buying a new Mac, since performance was very bad. 
Every kind of application was incredibly slow to open, even working with more than one app at time was impossible. Also just opening a simple PDF took a lot of time.

At the end, I decided to install a SSD on my Mac. A new world. Now everything works properly and my laptop seems to be reborn. I also updated to El Capitan and performance is even better.

So I advise you to buy a SSD, before giving up with your Mac. I have a Samsung SSD SATA 250 GB and I am very satisfied. You can spend less that 120-130 $ and you will have a completely new experience.