[maxerickson]

That's more or less what the 'basic' is aimed at, part of the idea is to set the income at a level that has a limited impact on the incentive to work.

Chart 3 shows quite some growth since 1980, but the per year increase is not exactly astronomical (and the page mentions that there are trends not accounted for in the data, such as the aging of the baby boomers).

It's also reasonable to expect a contingent benefit to have more impact on the incentive than an uncontingent benefit.