I had my 1983 injectors cleaned and "balanced" at a well-known specialist at about 150k mi and they came back looking like new with a report showing that they were rather unbalanced (different flow rates) as received and one was leaking slightly, but were now within a small tolerance and had nice even spray patterns.

Result?? I kind of felt (placebo effect?) that starting and idling might have improved a bit, but overall fuel economy was unchanged and the sparkplugs looked no different than before...all a nice tan colour on the insulator and the usual slight carbon deposits on the end of the threaded shell.

I'd say that if you have been using quality fuel (they all seem to contain their own form of cleaners), there's no need to spend on supplemental cleaning of the injectors.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.