Personally I'd be very careful (and I say this as someone who is planning on moving our own Yr2 DD this year). Slightly old-fashioned and shabby doesn't necessarily equate to a worse education or experience, and we are actually trying to go the other way - from a slick, very results and data driven school to somewhere a bit more nurturing and homespun.
DD is very academic, but we've realised that her current school's cookie cutter approach (focused almost solely on results in core subjects in the Year 6 SATs) leaves little time for anything creative or sporty, and it's already giving her some anxiety issues (she has perfectionist tendencies anyway). We are planning on moving out of London, where most of the local schools take a similar approach, to somewhere where the primaries don't achieve quite so highly on paper, but are more nurturing and holistic in their approach - forest school, lots of art, music and drama etc. We've looked at results further down the line at secondary level, and it seems that the slightly gentler approach at primary level has no detrimental effect on achievement in GCSEs etc - outcomes are just as good. Often the 'slick' schools are just teaching narrowly to the test, not offering a genuinely well-rounded education.
I get your concern about after school clubs, but again for us it's very much about quality not quantity. DD's school has a fair number of after school activities, but they're all bought-in franchises that are very variable in quality - nothing organised by the teachers themselves (not blaming them - I used to teach myself and know teachers have no time). It all seems very 'superficial' - looks all nice and shiny on paper, but when you dig a bit deeper many of the activities are low quality, taught by very inexperienced staff and basically just additional childcare. The kids often aren't gaining very much from them. Again, the schools we're looking at offer fewer club options, but those they have are run by teaching staff who know the kids and have some expertise or a genuine interest in that area. More homespun, basically.
I'd say friendships are key here - the difference with us is that DD has never really settled socially at her current school. She's not actively unhappy, but only has one friend who she genuinely seems to care about, and could take or leave the rest of her current class. If your DS is settled with a firm friendship group it is a very different calculation I think.
Would there be an opportunity to visit the alternative school again (maybe moonlighting as a prospective Reception parent on a group tour?) to give it another careful appraisal?