Ask lj: just how important is 30 Watts in your subwoofer?

I'd like to get a sub woofer. I'd like to get one that fits under the couch. That restrics my choice of subwoofers significately. There is a low profile yamaha that seems to be ok (not great) and fit the bill, The question is it comes in 100 wattt and 130 watt flavors, which a corresponding price hike. So my question to people who have had experience with subwoofers. Will I notice those missing 30 watts? I'm happy to shell out the extra money (my main speakers in my sound system are ~13 years old at this point, so a little extra just isn't going to matter if I keep the woofer for as long) but only if I'd notice the differnce.

dear car...

I love my car, mostly. The biggest gripe I have about it right now is it LOVES to turn the A/C with out my permission. Yes I know the window will defog faster with it on, but sometimes blowing air is good enough and I'd like to save on gas milage, please.

EDIT: I still remember the days when you could spray fluid and not have it wipe. I guess it is just a sign of the times. *sigh*