I don’t understand what your parents have against it. Maybe they think you’ll have a big deal with a registry and gifts? Because you certainly don’t have to, that’s not what its about. Its about the sacrament of marriage, and the recognition of your vows by the church and not just the government. But I don’t think a party afterwards would be tacky, I think a celebration of your validation would be perfectly appropriate!
My husband and I are having our validation done within the next few months. We are just now converting though, so that’s why we’re having it done. But its very common to have a secular ceremony, then a religious validation afterwards. Its not another wedding per se, just a validation so that the church can recognize the union as a marriage. Let’s say for instance you got married by a captain on a cruise ship. That’s a lawfully binding marriage, but its not a religiously recognized one – you’d have to have your vows validated when you returned.
I hope that helps. I would encourage you to talk to a priest yourself though, and maybe even take your parents with you so that they’ll understand the reason behind it.