I'm going to chime in on this one. Pickled herring is typically not used in cooked dishes (and Janssen's Temptation typically uses sprats [Swedish anchovies]). The brine for sprats is a sweet-sour brine, not an oil based on.
I was once asked by a friend who was going to Stockholm how I ate pickled herring...off the fork, straight out of the jar. Pickled herring has been part of my life as long as I can remember. It has been a staple in my mother's fridge for as long as I can remember. It is often on salad bars at restaurants where I grew up. In high school, when a friend and I would take road trips, jars of pickled herring and baby dill pickles were our road food. I only eat it the first day the jar is opened...I can't stand it after it has sat in the fridge after it is opened. That's why I buy the small jars. Dutch rollmops are not the same as Scandinavian pickled herring. And as much as I love pickled herring, I hate matjes (sp) which is served on a bed of ice with lots of lemon. My favorite pickled herring is the one that is in aquavit with peppercorns...my least favorite is with mustard--except on dark, dense rye bread (I can't eat that one out of the jar).
However, since pickled herring is such a big part of the cold table of a smorgasbord (I try to have at least three different kinds of pickled herring on the table when I do Christmas smorgasbord) and will have at least two salads made using pickled herring and perhaps herring pate on the cold table, and Janssen's Temptation is always part of the hot table.
Scandinavians typically don't eat cooked pickled herring--probably because so many other varieties of fish are available. And, whenever I've made or had Janssen's Temptation made by a Swede, it has always had canned Swedish sprats, not pickled herring in it. But, I have seen recipes that say if you can't get the sprats, you can substitute pickled herring. If I were going to substitute herring in Janssen's Temptation, I'd probably go for smoked herring...
As for reusing the brine, you can try putting onions in it. I've never reused the brine.
I know we have some Norwegians on the list, and TaxLady can probably share some other ways of eating pickled herring, I eat it the way the Scandinavian descendents in MN eat it. My DH isn't terribly fond of it, so I have to make sure I'm going to eat almost all of it if I put it out.