Some things to consider here:
(1) We are at the top end of a trading range between roughly 800 and 1600 in the SP 500 that goes back 15 years. There is no evidence at this point whether we will break out to the top side, or top out and make another trip down to the 800 region (which has happened twice before).
(2) During the period we have been in this trading range, Pimco's Bill Gross has outperformed virtually every stock fund with bonds, and his Total Return Fund is the largest fund in existence as far as I know (I am an investor in this fund).
(3) Companies are making record profits, but earnings momentum has clearly peaked. But at the same time, real estate momentum is on the upswing in a big way.
(4) The majority of highest performing stock mutual funds for the last 5-10 years are small cap funds.
(5) Top US hedge funds are moving assets from NA to Europe, as the returns in Europe are expected to be higher, and perhaps significantly higher.
(6) When John Q Public jumps into the market tends to be a very risky time to join. Public investors are always late, and flow of capital for stock funds since 2007/2008 didn't turn positive for the first time since January of this year. Beware.
Simply going out and buying NA stock funds at this point is rolling the dice. The market has not been much higher than now for a long time, and this could continue for a long time--or it could end in a breakout next week. But at this point, it is difficult to see where the earnings to put the market in a new era are going to come from. If you are going to do it, you will be safer with a "asset allocation" mix of small caps, bonds, and cash or international.
You can simply be patient, given that your returns are likely to be limited until something changes. If the market does break out above the current trading range, go with it. If it tops and goes back down, assume you are going to see the 800-1000 region again, and simply wait for the party to begin again.