Sound thinking.
There are plenty of decent alt-coins out in amongst the shitcoins that have far greater utility than BTC.
As the market matures I expect to BTCs dominance continue to decline, although I cant rule out the possibility it will still be around in some form or another in 10 years time.
As you mention, the wise play is to hold onto a portion of BTC, probably somewhere in relation to its given market dominance. i.e. BTC 50% market dominance, portfolio 50% BTC. If this falls to 30%, then adjust holdings accordingly.