No...? Is there another acceptable answer for this? In which cases is such an "upgrade" slowdown acceptable to the customer?
[EDIT: Changed most to many. But I think arguments about whether or not speed matters are silly in the general case. Arguments about tradeoffs are always going to be so specific to your app that a general argument is fairly meaningless.]
In exactly those cases where the customer cares more about the added benefits (e.g. security, maybe more features) than speed.
For example, I use firefox even though I've noticed that Chrome is snappier because Firefox comes with addons that provide features that I cannot do without. In this case, I have made a tradeoff between speed and features.
CPU is vastly cheaper than programmer time. There is a point where the tradeoff becomes unprofitable, but to prioritize code speed over all else is a recipe for terrible software.
If you're doing number crunching or heavy 3d, then it requires further thought, but if the code in question isn't one of your CPU usage hot points the conciser code is totally worth it.
It depends on how the slowdowns translate to absolute slowdowns in human perceptible time. Which depends very much on the kind of problem, and whether a piece of code is on the "critical path" for anything.