I had a Macbook Pro 13" Mid 2009 that was starting to go really slow. When I got my new rMBP15" a couple of months back I decided to "freshen up" my old one and give it to someone else so I got myself the 8GB ram and an SSD, put it all in to the old crappy macbook and made a fresh install of Mavericks. Guess what? It's went from "old and crappy" to "slightly used" and it's now booting in a couple of seconds and is superfast again!
My brother threw away his PC from 2012 when he got this, a 3 year older machine than his previous. And he's telling me everyday "What an upgrade from my old PC!!". So yeah, defiantly worth the upgrade.
Although the SSD I used was kind of overkill since that old macbook couldn't handle top speeds for it, it's still a big upgrade from an old standard harddrive. The RAM also makes a huge different when running Mavericks.
I'd say go for that upgrade and then perform a clean install of OSX and you got yourself a really nice macbook once again.