Diversification and rebalancing is a major plus. Currency fluctuations are normal and helpful. Note that, when the pound fell, the FTSE 100 went up - because the 100 is quite global in composition.
Also, if you happen to look back to 2010, the pound was as weak or weaker. I came to Canada in 2010, and in the next couple of years it hit sub 1.5 CAD to the GBP. Now it's at 1.72, after topping out just over 2:1.
Yes, being on the "thank fuck my money isn't all in x" is nice; but, if you're American and internationally diversified, it's probably "hurting" a little now - in USD. When the GBP was high, my net worth - *in GBP* - was much lower than it is now. Doesn't help me now, living in Canada (still tracking mine in GBP not CAD... shouldn't have started in pounds but oh well. When I did it, my major asset was one house in the UK, so it made sense I guess).
In short: over time, it shouldn't matter if you rebalance every so often, assuming your economy "reverts to mean".