Welcome back to the hobby!
There are lots of people here who know lots to help you. I have spent many hours just reading the old posts on here enjoying the pictures of stamps and covers and the information shared. I go by the old saying: The more you know the more you realize there is to know. And here is an excellent place to learn some more of most of what you might want to know about stamp collecting.
The 'printing marks' and 'coloured bars' (sorry, English as she is spoke in Canada, eh!(ay)) on your blocks of stamps are also known as Inscription Blocks (having information 'inscribed' upon them about who actually printed the stamps and designed them).
The coloured bars or dots or other rows of colour are sometimes known as Traffic Lights (Great Britain stamps) and are collectible just because they are there, or are attached to the stamps. Their purpose is to give the printers a reference and a check so they can tell that the stamps have been printed properly.
I like some of the Canada colour bars; the $5 Moose stamp block of 4 has moose hoof prints as the colour dots, I think the arctic duck and jellyfish stamps had a thermometer on the sheet as the colour dots, the idea being to blend a printers need into the design of the stamp sheet. It works and is really neat! It's like the moose was leaving his hoof prints in the cement sidewalk before the cement dried.

Go moose, go! Yay!

I think it makes the blocks or sheets more attractive and desirable and collectible.
As for investing I think the rarer the stamp and the stamps with the least copies available to the collectors seem to increase in value over time as more collectors want the dwindling amounts of the same supply. Buy cheap and sell dear, as the old saying goes.
Usually for me though, it was buy at whatever price because I Had to have it and then, when I realized I had spent too much on too many, sell for whatever price the market would give me. I am not a good investor, I am a good spender!

Lets see some pics of what you have and people could suggest ways to go from there. What is it you have now? Mostly blocks of different sorts? Old, new, mixed? What country(ies)? How is it stored now? How do you want to store it, or think you should? Questions, questions. Or, what are your questions? People here love to share their knowledge. Ask away!
