Yes it's worth it, just for boot/loading of app times alone. Everything, including running virus/malware scans, backup, Windows Update, runs much faster. Even those with SATA II MB's will see dramatic performance increases.
Since installing Windows 7 Pro on my first SSD, a Crucial M4 purchased in late 2011/early 2012, I don't care to run on platter drives again, even the SATA III ones. On a SATA III MB, a SATA III SSD does everything nearly 3x faster than on a SATA III platter drive.
Just my two cents worth.
Cat