SSDs? No way...
Please don't try to justify the upgrade to SSDs. Companies that rely on heavy storage usage, either on a wall-to-wall rack or on desktops would have high-spec machines already, with high performance storage anyways, before the introduction of SSDs. Only top notch, elite desktops would have this kind of upgrade justified. On notebooks, only rugged usage would justify that. For regular usage, you can buy 5-10 times more storage and a SATA controller wtih any form of RAID for the same price of a single SSD.(considering retail prices). Do you work for WD or Samsung, by any chance?
On the other hand, memory upgrade is a charm on outdated machines. I mean, really outdated. Provided you can find the old memory, a machine with 512MB that can jump to 2GB will increase performance 8-12-fold. I tested it myself on a number of occasions. Chances are, these crusty old PCs will be running Win98 or XP or some proprietary OS or software in exclusive mode, in the back of a warehouse, gathering dust or something, and are surely already using the world famous disk-swap-HDD-LED-always-lit-up scheme, and they've been doing that for the past 5-8 years. For people with really tight budgets, memory pays off.
SSDs are just a fad, where high performance is essential. It would never justify to take a 5-year old machine and slap a SSD in it, not upgrading anything else. Chances are, there are even no SATA controllers on it, to begin with. Outside the top (boss) notebook, it is a Catch-22 to justify this sort of upgrade.