great points all around.
the writers did seem to become 'bored' with the present day characters or if not bored they didn't really know what to do with them for many of the reasons pointed out here.hence there was alot of floundering.
in some ways i find it 'comforting' that the core characters essentially remained unchanged in the present.a little constant in an insane world.but it does prove problematic when trying to come up with compelling storytelling.
i too noticed the lack of direction for the original cast as soon as the story returned to the present after 1795.
they drifted about the perifery of the plot for several months before being somewhat returned to center stage during quentin's haunting of collinwood.
it is interesting to note that the core family didn't really change in the present.not only did they need to emerge from every crisis unscathed but essentially they always forgot about it entirely.for nearly a year the adam plot consumed everything and eveyone around it but as soon as it was 'done' and the plot shifted to the quentin storyline everyone acted like none of it had happened at all.which is pretty remarkable when you consider what everyone went through during it.it's also true that david wasn't really allowed to grow up in a realistic way.i started to notice that as soon as maggie took over as governess.he seemed too old even then to be babied by a governess and in real life would have been sent away to school.
it was questioned here why they didn't make the collins family bigger in the first place.why not more siblings and children?my theory is that the show started off with as many characters as it could to establish itself.over the proceeding months a few more joined the fray:mrs.johson.jason mcguire.willie loomis.
then the character was introduced that would fundamentally change the whole format of the show:barnabas collins.after barnabas dr.julia hoffman was the last major "human" character that was allowed to take root on the show in the present.look at the characters that come to center stage after her.they are either supernatural by nature(angelique,adam,nicholas,eve) or by influence(quentin,tom/chris jenings).once it became clear that the supernatural edge was bringing in the ratings the produces didn't bother to introduce us to 'regular' human beings in the present fearing that they would probably read as 'boring' to the viewers responding to this new hook.thus when characters like burke,victoria and joe depart they aren't really replaced by comparable characters.why date a fisherman when you can date someone trying to create a master race dedicated to satan?this thinking was perhaps short-sighted and misguided.
at the same time the writers must have recoginzed that the original family was important to viewers because as has been said no matter what disaster befell them they always(for the most part)emerged without a hair out of place.