I once_a_teacher, I can answer some of these questions.
I actually agree with you that research expires faster than teaching does. To be a competent researcher you have to be up on the latest literature. When you start a new research area, this is a huge time cost, but when you are active in an area, it's a breeze. If you take a break, you will get behind fast. With teaching, you'll do best when you're teaching in the very research area that you know so well, but you can also be very effective if you carefully read a couple of textbooks on the course you're about to teach. There are also pedagogical advances, but these aren't so hard to keep up with, and you won't be implementing every single technique anyway. The pace of change within a particular course is not nearly as fast as research. It's easier to keep up with it after a break. Especially if your topic is statistics or history of psychology!
As far as juggling projects goes, at my SLAC I juggle 3 courses per semester, service work, advising (30 students load), and usually about 6 research projects, sometimes on widely different topics, involving 1-4 students each. I have MORE lines of research and more projects than I did as a postdoc. When you're working with undergraduates you're more likely to have those lines of research be very different from each other rather than have them be programmatic, because you might be the only "cognitive" or "social" person at your school. So you'll take every student doing any project in that area. (Note: there are ways to be more strategic about this and force students into programmatic research, but you will at least be encouraged to branch out more. Personally, in spite of the challenge, I very much like broadening my research areas.)
At an R1 you might technically have more projects but they'll all be on the same sub-topic of an area of psychology, with extensive overlapping literature. If you ever want a grant, you have to work this way! I still don't think it's more work to be at a SLAC vs an R1 or anything, but there is this myth that it is definitely less work to be at a SLAC, which is obviously false. And yes, if I were evaluating a postdoc (or research scientist) vs. an assistant professor applicant for another assistant professor job, I'd want the postdoc to be publishing at a faster rate because that applicant doesn't have all of those other duties.
I think that DocJ's point about advising is definitely school-specific. At a lot of R1s, faculty have no official academic advising duties. They surely may provide unofficial advice to numerous students, but they might not have an "advising load." Those duties might be carried out by a centralized advising office. Also at R1s, even if there is an advising load, the culture of the institution is typically that you have this list of names but you might never meet the students (that was the case at my undergrad.) At a SLAC the culture/expectation is that some of these students (and people not on your list) will regularly stop by your office and have hour-long conversations with you. But on top of that, you might also have a longer list of people that you are officially responsible for guiding through the course selection, graduation, and job/grad school process.
At my SLAC in Psychology we all have 20-60 advisees, but in other departments faculty have, like 5, because the student-faculty ratio is not equitable and psychology is a popular major. The overall culture is that students meet with their advisors at least once per semester, but it differs for each faculty member and across departments. Those with better ratios might have much more personal relationships than we do with ours. At wealthier SLACs the student-faculty ratio is better than it is at mine, so the advising loads are lighter.