Non-startup speed benefits from replacing HD with SSD?

I started a thread the other day about what i need (RAM vs SDD size) if I decide to get a MacBook Air, but I have another issue I've been thinking about lately.

I have an early-2011 15" MBP with a 2.2 Ghz core i7 and 16 GB of RAM. I've debated about swapping out my current HDD with a SSD. Aside from the typical mail and multi-tab internet browsing, I typically use my MBP for Office (multiple small/medium sized files), Quickbooks via Parallels, Evernote, Lightroom 4.1, PS CS 6 occasionally, and Nik plug-ins. Lightroom, PS, and Nik plug-ins are clearly where I wish I had more speed.

For Lightroom, I have a 1TB external Thunderbolt drive that houses my photos and catalogue. I'm guessing I have 35,000 photos in the library. I'm currently using about half of that Thunderbolt drive.

I have no question at all whether a SSD will speed up boot and application launch times. I'm sure it will. The thing is, I don't boot up my Mac all that often (but I do free up resources by typing "purge" in Terminal on occasion). So my question is simple. Will a SSD result in appreciably faster overall speed when using programs, hopefully LR/PS/Nik, but even things like Parallels and Excel?

Thanks,

Steve