It should be a priority, though. Firstly, because it's not just about testimony, but withheld documents. Secondly because if they want to lie and/or plead the 5th, then let them do that and get them on record as doing so (and allow the twittersphere to publicise all those Trump quotes about only guilty people pleading the 5th). And, thirdly and most importantly, if you don't enforce subpoenas then you're sending the message that subpoenas are meaningless and that anybody and everybody is free to ignore them from now on, as well as the message that Democrats are only bluffing in everything they do.
That's bad for the Democrats, good for the criminals, bad for the US right now, and bad for the US in the future.
It's also worth noting that pleading the 5th is not guaranteed. Sondland would probably have done himself some favours had he pleaded the 5th, but instead he sang like a canary (eventually). I think that the majority of Trump cronies will do whatever they think is most likely to best serve their own self-interests.