I am not a hardcore packet collector, but I do like to keep packets sealed at least one or two, hoping they might be worth millions in 30 years!

Anyway, I do not think packs can be considered as a huge investment, especially mass-produced collections such as World Cup from the 1994 until now. I mean, you can get a pack for 0.50 and in 10 years it might be wort like 5$.
On the other hand, packets from vintage collection can go up to few hundreds in value. Its hard to predict if its going to be worth something in future, but as long as I enjoy it, I do not care how much its going to be worth. Its worth to me, do not care about its value to someone else.
I still keep my pack collection messy, in no particular order. Probably because I do not have many of packs left. I gave a lot of the packs to my nephew who thought it might be good idea to collect them, and gave up after few weeks. Recently I wanted to sort them out, and took a photo which you can see bellow.
In general pack collecting can be really interesting hobby as long as you focus on it. There are so many variations of packs.I know the Ukrainian collector who (I guarantee) has thousands of packets. He only collects packs though. I might try to ask him to come to the forums and post some tips and stuff. Not sure if he speaks English though we communicated via Google Translate.