I don't think it matters one way or another. Nothing is going to prevent the US and UK from trading with one another after the Brexit.
A stronger dollar vs the pound is just going to mean the UKs exports will be cheaper for US customers, while US exports will be more expensive for those in the UK. Of course this is going to hurt companies who export to the UK, but don't really consume UK goods (for example, Apple). However, it helps companies and individuals who do alot of importing from the UK, but little of any exporting to the UK. Offhand, I can't think of any companies like this, but according to US census, these do exist to the tune of $57 billion per year (vs $56 billion for exports) https://www.census.gov/foreign-trade/statistics/highlights/top/top1512yr.html, so its probably a wash
As for the UK's "voice" in the EU, can you give an example where it has advanced US interests in the EU? I can give at least one non-example, with the that GMOs, which the UK seems about as opposed as most other EU countries