I have an Indian passport with valid US-visitor visa. Will I be allowed inside US after travelling to Iran now- having done so several times before?
Traveling to Iran would make you ineligible for the Visa Waiver Program (you would need to get a visa). But since the you're an Indian citizen, you aren't eligible for the VWP anyway (unless you have another citizenship you're not telling us about), and in fact, already hold a US visa.
Therefore, there is nothing that would prohibit you from coming to the US. It is, of course, possible that you could receive extra questioning at immigration, and if you're seen as a security risk, you won't be admitted. That's always true whether or not you've visited Iran though, but there are reports of people who have visited Iran being singled out for questioning. A visa is never a guarantee of admission.