Management - probably not - but there was a mechanism whereby letter feedback played a role in decisions. The best example I can think of was Cloak and Dagger in PPTSM 64. They proved popular enough, and Marvel got enough feedback, that they promptly appeared again in PPTSS 69 and 70, and then again in 81 and 82.
My recall of Venom was that he was 'grassroots hot', but not overtly hot like Punisher, Wolverine and Ghost Rider. Readers loved him. Obviously Salicrup knew this, as he wanted to save Venom for use in ASM. That grassroots love took some time to manifest in market heat, though. Early on, ASM 298 was a bigger book than 300, and 312 was broken out (Hobgoblin vs GG) before 315-317.