Tons of memory but applications keep needing to be "paused" or shut down because of memory problems?

Question

About 6 months ago I upgraded to 16GB RAM and have had no problems.  Have checked the system report for my memory and it says both of them are OK.
Within the past 2 or 3 weeks I've been seeing crazy lagging at odd intervals with a message coming up that because of memory overload (next time the message comes up I will try to screenshot or at least remember the exact verbiage), some applications have automatically paused and basically recommending I force quit.  This happened even today after my computer had been completely turned off all night and I only opened up my mail client, Skype and Firefox after turning the computer on.
I just installed MemoryKeeper and can see I'm usually sitting at about 10GB up there, but every now and then (at completely arbitrary points - not even when I'm using memory-intensive processes necessarily, but maybe just writing an email), it'll jump up to 20GB and even something outrageous like 300GB for a second (?!????!?) and then the screen will come up saying that some applications have been paused out of necessity.
I'm assuming something is corrupted somewhere but between all the constant updates programs are having me do (running Firefox 28 in case anyone's aware of a problem with that), it's hard to pinpoint exactly where the issue lies.  I really don't have too many applications: on a given day, I am using Firefox, Safari, my mail client, iPhoto, iTunes, and maybe something like Lightroom or Premiere (but hey, I got this MBP with the specs I got so I could do some editing, and have done it without issue in the past so I doubt it's my system specs).  I am pretty good about not really loading a bunch of apps on my computer and periodically cleaning out things I haven't used in a while, and my hard drive is new-ish as well at 1TB with about 500GB remaining available.
Any ideas what may potentially be causing this issue or what I can do to resolve it without taking it in and having the store charge me a million bucks to tell me to buy a new computer?

Answer 1

I'm really sorry, I have no idea where I got 10.6.7 from (I think I was going off my old system information from the last time I used this forum).  I'm using 10.9.2.
So the issue seems to have started around the time I installed Maverick (although not 100% sure on the timeline, but that's what I believe to be the case).
Additionally, I just figured out that the problem consistently starts when I use Spotlight, whether to search for items or to do calculations.  If I clear the fields fast enough I don't have any problems but if I leave anything in the Spotlight field and resume using other applications, my memory jumps up and I quickly reach a point where I have to restart my computer (it would be too late to simply clear the field).
I don't know if indexing is the problem since after doing a massive indexing when I installed the OS, I don't notice that it is doing it anymore.  The problem seems to be caused only by having characters left in the Spotlight field.