First, even if it is SATA 1.5Gbps, it's still a great upgrade, and you can take the SSD with you to your next machine - the SSDs Apple is shipping in the MBPs are not very good, and you'd be better off buying one separately anyway.
Second, which MBP do you have? That definitely doesn't sound right - I have a non-unibody 17" and it only takes about 5 minutes to take the top off; it's mainly just 12-18 screws, and the 15" looks identical to me (unless they changed how it's put together later on):
http://www.ifixit.com/Guide/Repair/Installing-MacBook-Pro-15...
The big win with an SSD, even with a 1.5Gbps interface, is the seek time. It's amazing how much faster simple things like "du" are with an SSD vs. a spindle.
Seriously, if you can at all stomach opening your laptop again, a 120GB-240GB SSD will make it seem like a brand-new machine. For the first week or so, you'll start ten applications at once just to watch how they all come up with no bounces on the dock. :-)
The downside is that the model of MBP that I own has a SATA interface that is limited to 1.5Gbps and the research that I did showed that the best SSD's are faster than that, so I'd be wasting some of the power of the SSD because the interface is slow.
The other problem is that installing a replacement hard disk in this machine is a nightmare. I've installed thousands of hard disks into computers and this was the hardest and most scary - I had to bend circuit boards and components to get a new 320GB/7200RPM disk in to replace the old 120GB/5400RPM, hoping that nothing snapped. Apple must have tried hard to design a machine with a disk that hard to upgrade.
Given those two issues I think I'd probably buy an entirely new machine and give the old machine to someone else in the family.