Love2LoveYa sounds like it could have been on the Original Doll album (the one that was scrapped).
Her dancing has gone downhill because:
1) she has had knee surgery twice (once at 18, then again in 2004)
2) she is 30. the last time she really danced was 2004 Onyx Hotel tour, which was 7 years ago when she was 23. and the iconic routines we remember are also from years ago, like Slave (19), Oops (17), Me Against the Music (21). everyone moves better when they are young.
3) she is not as fit as before. this is going to affect her ability to dance, just like it would in sports. J.Lo is 40 and goes at it harder than Britney but she is in better shape (despite also having 2 kids). You have to train to be an excellent dancer and I don't think Britney is interested in doing more than the bare minimum.