I would bet that IndianGoldEagle is more of a coin person than a Paper Money person. He may have forgotten that this is the Paper Money section

As to investing, it's not much different than in any other collector items. No matter what your collecting condition is all important. I would treat any Paper Money collection as a looong term investment.
Coins on the other hand, unless your a real collector can be governed somewhat by the price of precious metals. When Silver and Gold go up your coins go up, you may as well be watching the stock market.
I would much sooner learn how to grade than pay a bunch of money to someone else for their opinion. Use the bunch of money you save on grading to buy more nice notes.
The way I see it is that a lot of the guys that are buying graded currency don't know how to grade and seem to be more than happy to pay someone else to do it for them. I think there missing half the fun of currency collecting, but if your not a collector and just investing the fun part of collecting and learning how to grade wont interest you. If you do learn how to grade, and it's not that hard, you can do some better buying.
Buy raw notes at the right price and you will do ok. When it comes time for you to cash in try selling them to collectors that know how to grade and you should not have a problem.
The last thing I would do is have them graded when it's time for you to sell, at least it will be current grading, remember what IndianGoldEagle said, grading has changed over the last 20 years. Yesterdays Fine may be today's Very Fine, and of course yesterdays Very Fine may today's Fine.
Just goes to show you, cant seem to depend on the guys getting paid the big bucks to grade. And of course if you do end up buying graded currency DO NOT buy the holder the note is in, I don't care who's name is on it, buy the note that has the eye appeal.
I can show Photos of graded currency that not many collectors would want in their collection, but it was graded high by some of the so called "best" graders.
Bill Collector