Anyway, I just got the final Shinkenger CD, Zenkyokushu - and this is what I was waiting for. It has every major vocal song on two disks, including new character sung songs, sound effects from weapons and Origami robots, and music from the Shinkenger vs Go-onger movie.
It's simply the best deal for you're money, which now makes me wonder if I really should wait all year to get the final music CD for Goseiger. That's a pain to wait so long, though... ANYWAY - there's you're ultimate tip - wait until the series is over and get the final CD version. Second best, for your money, is Volume 2 of Sentai Series Music, which is sort of like the mid-way point for a lot of their major songs. Also, always try to hear the actual music from the CD before buying it, to insure no mistakes, which you can do by finding the CD you want at CDJapan and listening to the samples.
I hope this might help someone. The music on Zenkyokushu was definitely worth it. Samurai Ha Oh is my favorite of the tunes.
You can buy Zenkyokushu at these links