If you see the last 10 years EEM has not done anything (.6% on price, .77% on NAV), while SPY has performed (150%) spectacularly.
The PE of EEM is 11. Separately, I think at some point US will be hit by recession, on the other hand India, China, Taiwan, Korea, Brazil (mining, materials) all expected to continue to grow.
The below graph shows the correlation between UUP (dollar index) and EEM performance. For almost a decade US is getting away with printing Trillions of $$$, and at some point it is going to catch up with it. If you think King Dollar may need to take some downtime, that also should work in favor of EEM.
if you are someone looking for diversification, or believe asset allocation, you may want to consider EEM.