Arnold
If you planned your flight properly, and navigated properly, you'd know your heading and track, within a couple of degrees, and you'd know your groundspeed within a couple of knots, absent a compass and absent any GPSs.
If you checked the accuracy of your altimeter/s, in accordance with AIP, at the commencement of your flight, you'd have a good idea of the accuracy of the reading/s. If you have a transponder with Mode C, you can confirm the accuracy of the reading/s at altitude.
If you couldn't manage to do a few circuits in your RV7, without an airspeed indicator, you don't know your aircraft well enough.
I'll say it again: It's not about the desirability of serviceable and accurate instruments. It's about the presumption of innate incompetence and criminality of Australians, mixed with scaremongering that plays on the fears of ignorant punters, that has produced the regulatory Frankenstein destroying GA.
The experiment has been run in the USA and the results are in: The Australian approach is a complete overkill (literally).