Capt PB...
I've often told Pilots that "Standard Speeds Apply" or 250 kts (or whatever) at the SLP, and yes it does sometimes use up precious RT time when we're asked and the freq is busy.
If I need you to fly a particular speed I will say so. By the way, I, and my colleagues, don't use speed control for any other reason than to help YOU and everybody else in the sky get organised into a nice sequence to improve the landing rate. Even if you end up in the hold, as well as being 1000ft vertically separated you'll be spaced laterally as well, instead of being slap bang on top of each other. This makes taking a sequence of a/c off the hold much easier. So, when you are "speeded" and still end up in hold it really hasn't been a waste of effort, honest.
From your post I know that you appreciate this but it seems to me that some of your fellow pilots don't.
As McD says above, if we say nothing STICK to the SLP, if it's busy DON'T askl, and if we give you a speed try to fly it as accurately as possible.
Rgds BEX.
P.S. LACC at Swanwick has extremely accurate Ground Speed readout now.