I prefer to think of things in terms of probabilistic prospective returns......in that context US indices.......specifically their current operating earning multiples and then the underlying profit margins of its constituent companies are at historically elevated levels.....by some measures about as high as they've ever been
So probabilistically.....one would not choose these levels......if you we're seeking say the 9- 10% historical annual returns that US markets have enjoyed in the past to play out for the next decade....to do so, to get to that 10% annualized return.....would require somewhat implausible things to happen from right here, right now:
(1) that investors, paying already elevated multiples of earnings, would decide to pay even more.....such that you would get continued sustained earnings multiple expansion on top of earnings growth that would plateau at some level higher than where we are today or have sustainably been ever....I'm not saying this cant happen in the short run.....markets can trade anywhere at anytime before returning to rationality.....SPY/QQQ multiples can go higher in the short or even intermediate term.....but they've historically never persisted at these multiples for any great length of time....in periods where multples we're elevated the general stock price level has been sustained and grew in these instances by underlying profit growth (margin expansion etc.) such that multiples came down as the earnings expanded.......but today we get to no (2)
(2) that US profit margins (already historically elevated) would expand further from here.....we are in quite rarified air in terms of margins....that they would expand from here to support stock prices as say the underlying earnings multiple contracted to more average level also seems implausible.
Valuation is not a short term timing tool......rather its a probabilistic expected return tool... probabilistically.....expected 10yr returns are low for US indices.....when you overlay the fiscal situation in the US....running 6-7% budget deficits during a period of full employment....what you also realize is that the US government via borrowing & spending is stimulating US economic activity at an unprecedented level for peacetime....and in a very real sense this fiscal borrowing is flowing through to US corporates as elevated profit margins and profits...and to the public as excess liquidity from which they can speculate on the stock market in their 401k's and Robinhood accounts......whether this continues or not will have a large bearing on what happens next to earnings and folks enthusiasm to buy a claim on those earnings.
For an Ireland based investor......SPY & QQQ....present real challenges IMO...everything I've highlighted above.....to which you can add currency risk......given the current EUR/USD exchange rate....which again is at something of a historical high (albeit SPY/QQQ has some natural hedging given the international earnings profile).
I say all this for the indices......there are plenty of companies that have plausible and probable avenues to provide an investor with high single digit 10yr returns.....and assembling a basket of these would make more sense than relying on expanding enthusiasm for SPY/QQQ right now