But those regulations would only apply to your trade with the EU, rather than to all of your business.
The advantage there is that it gives you the power to actually weigh differences between trading partners and see if one version works out cheaper than the other, in a way that you otherwise can't.
So you'll have the cost of meeting those regulations VS the price saved by better negotiation power. That balance will likely change from country to country and also business to business.
That's still a rather large chunk of business, especially for people who predominantly do business in the EU and without any say in future regulations. Your second point is the one big advantage I see, but I also don't see us having much negotiation power outside the EU.
We're a nation of 65 million versus a trading block of 500 million in the EU. We can make more targeted negotiations based on the UK economy, but when we enter negotiations, the power will lie with larger trading blocks/countries. I also don't fancy waiting around for a few years whilst our politicians sort out trade deals that may or may not be better than the deals we already have in place.