Go for it! The dealer I bought my CVT Insight from was selling it about the same price as the one you're seeing (14,998).
As for economy, expect to get around 10MPG less compared to the 5spd model as it doesn't include the lean-burn catalyst. A plus however is that the CVT models don't seem to suffer from the recal effect that 5spd models have.
Unless you really need to accelerate fast or need the extra "kick", leave the tranny in D mode. Switching it to S mode from what I've seen, increases the RPMs by about 1,000. You can tell if you're in S mode by looking at the green S light located near the battery SOC meter on the dash.
Your dealer is probably selling it cheap as it's been sitting in the lot for a while and they are desperately getting rid of it. I know mine was.
The Insight suprisingly does very well on hills. I've driven it in hilly downtown san francisco a couple of times and it has no problems getting around.
Also consider this. Knowing most dealerships (at least in california for me), the 5spd manual is almost impossible to find on the lot and needs to be special ordered. Ordering it from the factory will cost you about 17,000-17,500 (depends how nice your dealer is). You figure the money you save from buying the CVT at the price you're getting it for will more or less 'balance out' the cost for dino fuel.