I think that in Easy/Normal diffs, a maximum DS*SV (or sth. like this) should be set depending on the BPM, besides limits on them respectively. Either DS or SV does not presents the difficulty.
SV=1.2, ds=1.2* is greatly different from SV=0.8, ds=0.8*.
Well this is only my personal opinion, and perhaps it's not accurate.ok i've seen oko's post.
Spinner recovery time should be at least 4 beats.
I also have some questions on this. Maybe it's has been guideline for long, but I do not see it necessary to leave 4 beats. Surely in 180 BPM, 2 beats may be too fast for new players to handle. However, in some low BPM songs, 4 beats is really long. In these cases, if mappers want to put a spinner somewhere, it would make the rhythm of that part very loose and boring. At least, I think 2 beats is fine if the BPM is relatively low.
Also I agree with some of the ideas above.
I support Snowy Dream's idea of changing the minimum OD of Insane diffs to be 6/6.5.
There is Advanced between Normal and Hard, but it's usually still a gap between Hard/Insane when the hardest diff in the map is iconed as I. For the reason a Light Insane might be mapped, and in this case OD7 is kind of too high for it. If OD6 is considered too low, OD6.5/6.7 would also be fine.
As for the difficulty settings, I'd support on a looser rule. Depending on the songs, using a bit higher/lower OD/HP won't harm. Even songs with 180 BPM differs a lot.