One of the reasons extra income has a small effect on happiness is that we rapidly adapt to new luxuries. A fancy new Porsche will cause a spike in my sense of well-being, but I'll get used to it soon enough, and the happy effect will wear off. If we adapted completely to everything, then there would be little we could do to permanently alter our sense of well-being.
One thing you could do is consume more, faster. That is, buy something even nicer just before the positive effect of the last thing wears off. As far as I can tell the happiness investigators simply haven't seriously considered this option. There seems to be a kind of bias against transient pleasure. But if you're ALWAYS experiencing SOME transient pleasure, then you've permanently jacked up your level of SWB, even if EACH pleasure wears off.
One of the huge deficiencies of the happiness literature is that there is almost no data following individuals over time. So the data can tell you that, on average, buying a new car doesn't make people happier over the long run. But it can't tell you that always buying a new car before you get used to the old one doesn't make you happier over the long run. There needs to be more research on this kind of individual hedonic strategy.
Also, it turns out that we don't adapt equally to everything. So if there are things that we can spend our money on that will make us happier, and some of the effect will tend to stick, then more money could get you more happiness as long as the money is spent on the right kind of thing. The evidence shows that if you want to be happier, you should spend more time and money on exercise, meditation, and strengthening your social bonds. And It turns out that we don't adapt much to cosmetic surgery. Looking better makes us happier, and we stay happier. Especially with boob jobs.
So, here's my Benthamite policy proposal of the day: vouchers (and/or tax breaks)for breast implants.