Let's just talk about Si base vs Se base. I don't want to talk about Si/Ne vs Ni/Se, because then we are also including people with opposite strengths. That gets too complicated.
I think both Si and Se can be abstract but the abstraction develops in different directions.
Si painters can pay lots of attention to details too. I'm just saying that
if art is made purely with the Si function then the painter will focus on his impressions and downplay the object. Si is maybe not so much "emotional impressions", but more that sensations are felt deeper than in other types, because some unconscious "archaic experience" is attached to the sensations. Sensations are felt "from the inside". Deeper, more "genuine", a slight touch of the "numinous". I think that's not going too far.
Yes, I have a lot of concrete pictures in my pinterest. But I didn't paint those pictures myself. I have just chosen pictures that give me nice sensations, many have nature or a sensual feel about them. I do think there is Si in them but I have of course used other functions also when choosing them. Sometimes when I look at other people's Pinterest I am surprise how "sterile" they are, compared to my own taste.
I can't say much about Se at this point. My former art teacher is a SEE and
she has paintings online. Many of them are definitely abstract but I think there is an "Se feel" about them. What do you think?
EDIT: Also check out chapter XI "Definitions"
47. SENSATION, page 461 concerning concrete and abstract sensation from Jung's point of view.