Software like that exists (e.g. ibus, which creates a database and cache in the home directory), but generally I haven't had any problems with Guix on other distributions.
Ah, good to know. Just tried sbt (build tool for scala) with Nix (have no experience with Guix, but like that everything is in the same language) and it indeed creates .ivy and .sbt caches in the home directory. Everything else goes into the store like it should.