Very little. If you've had professional legal representation then naturally the legal profession tends to look out for them, but the compensation to defendants personally (and to other parties involved in a case, such as witnesses and jurors) for their time and inconvenience is negligible.

What else are you going to do? Stop issuing penalties for motoring offences

It is sad that you dismiss that possibility without even considering it. Our structure for penalising poor driving in the UK is woefully unfit for purpose:

1. Its sanctions aren't an effective deterrent for the relatively small number of drivers whose behaviour really is habitually unacceptable and likely to cause significant problems for others.

2. It penalises many generally good drivers for breaking arbitrary rules without any evidence that what they did was actually dangerous, or even inconveniencing anyone else.

3. In some cases, it even gives drivers a despicable choice between driving safely and driving legally, because obeying those arbitrary rules when they are obviously inappropriate under the circumstances will antagonise and/or inconvenience other road users. Some of those other users will then do something more dangerous, such as performing a risky overtaking manoeuvre, and while the law may say that the other driver is then responsible for the resulting accident, that is of no comfort to the innocent and now dead third driver who was coming the other way and wound up in the head-on collision.

5. It penalises many generally good drivers for minor errors that everyone makes at some point, based essentially on luck. If everyone were actually prosecuted reliably and uniformly for these offences, so many drivers would lose their licence within a month that the law would be brought down or the government would be. Because prosecutions instead happen only intermittently and the law is inconsistently applied, it instead serves as an effective fund-raising tool, often with a glaring conflict of interest where effectively altering driver behaviour would reduce revenues so the incentives are aligned with catching people out rather than deterring undesired actions, and it breeds driver resentment.

In short, our system does not effectively defer serious bad behaviour, while simultaneously penalising behaviour that may not have caused any real problem at all and reducing general respect for the law among a very large proportion of the adult population.

With the rise of automated penalties where no review by a human with common sense need even be involved, man is now judged (often erroneously) by machine, and as I've been arguing, that means the system causes wildly disproportionate distress to a significant number of completely innocent people. I don't accept your claim that the people getting off on these appeals were almost always there and doing something wrong really and just got off on technicalities. I've never seen any data to support that position, in contrast to numerous reports that would indicate otherwise and demonstrate beyond any doubt that these kinds of automated enforcement systems are often fundamentally flawed.

(Just to be clear: I have been a driver for many years, and never had so much as a parking ticket. I have no personal axe to grind here. I just think obviously broken "justice" systems should be fixed, not defended as if making something the law automatically makes it right.)