I had the SE110 and went to SE420. I found that even the SE110 had enough bass personally but what I didn't like about them is that they had no highs at all. The problem with in-ears is that the bass is totally dependent on how far you put in the rubber or other type inserts wedged into your ear canal (even if they instructions say not too, if I don't put them in far, they slip out with small rubber tips and the others are just unconfortable for me).
The SE420 didn't blow me away in terms of sound either (I just expected more) but the highs are much better and that is what I found lacking in basic SE110. The bass sounds almost as good as the Sennheisers HD 595 that I have....
I think that the problem with in-ear remains figuring out which tip types and sizes are best for your ears. The problem is that in certain cases (like sweating at the gym), they slip out all the time....
Enjoy your new purchase.