Macbook Pro upgrade (or not)

Hello all you beautiful people. I have an opinion to ask that I'm sure some of you might be clued up on...

I've got a 2009 13-inch Macbook Pro, 4GB RAM and 250 GB HD space (and two external hard drives now to help with scratch disks/backups etc, 250GB and 1.5 TB). I've been needing to up the specs for a year or so because it's quite disappointing when I need it most. Peak time would be when I've got Safari, Photoshop, Indesign, Sketchup all running, with something rendering in the background. Really slow, frustrating to use then. Otherwise day-to-day it's fine.

I need to apparently service the battery which is fine. I'm not worried that about the display being 13-inch, it does the job, graphically it's fine. I'm going in tomorrow to get it looked at and/or sent off, if I do, I'll get it up to 8 GB RAM and 500 GB. Cost quoted was roughly... battery [if replaced] (£75-100), RAM (£65), HD (£100-150) and service/sendoff charge (£75) so total between £300-£400. Another option that someone floated was to just to invest another computer as a main one (say an iMac with student discount around £1050).

Now I've only got another year of uni left and full-time practice would mean me working on either an office desktop or laptop that they would provide. So a personal laptop would be enough otherwise. Is it worth actually investing in a new computer or just upgrade what I have?

I really don't see the point in upgrading a 5 year old computer, especially at that price.

Can't you upgrade the RAM and the HD yourself?

Was in a similar position when my old 2009 (iirc) model died on me last year. Battery needed a service and was looking at a possible HDD replacement to get it up and running again. In the end I opted to just buy a new one up to date MBP 13" retina. Didn't see the point in investing nearly $400-500 into a 4 year old machine when I could put it towards something new.

hello ehmo.
long lost brother.

Sup dawg.

Spoke to a few people. No point upgrading laptop, will continue using it, but decided to invest in an iMac considering it's my last year with student discount...

iMac is a great investment, I also done a similar thing about 3 month ago.