The answer is somewhat analogous to Sir John Templeton's answer to, "When should I invest?" He replied, "When you have the money!" And the answer to this question is, "The wines you like." The challenge is to purchase wines today that you will like when you open them some years down the road. Most wines that you drink on a day-to-day basisunless you are Bill Gatesare made to be drunk within two or three years from harvest or bottling. A small percentage, maybe 5 - 15%, is made to be aged, that is, not to be consumed until five or more years after harvest or bottling. Some, like Vintage Port, many Bordeaux, Burgundies and California Cabernet Sauvignons, can be aged 15 or more years. Vintage Port lasts up to 50 years.
The first thing you must decide is, "Do I like the aromas, taste, food matching options that I get with these aged' wines?" How do you find out? It is simple: taste some. The LCBO, Vintages, various wine clubs and organizations in your area taste these wines periodically and you should be first in line. Or buy one older bottle at Vintages or through Vintages' Classics Catalogue and share the expense with 4 or 5 friends. That way, the $100 cost is divided 5 ways or $20 each. It might be an amazing experience well worth the money.
Let's assume you love it and want more. Let's also assume it was Bordeaux. You have the opportunity, twice a year, to buy aged Bordeaux via Classics Catalogue just as you did in your experiment. You also have the opportunity, once a year, to buy non-aged, not-ready-to-drink Bordeaux via the Vintages Bordeaux Futures offering. These wines can be less than one tenth of the price you will pay Classics Catalogue in 15 years for that same bottle, now ready to drink. Hence, the common reason why people develop a "cellar" in the first place.
In the end your cellar will become much more. It will be like a philatelist's stamp collection or a sport fan's hockey cardsa thing to ponder over, sort and organize, agonizingly decide which bottle goes where and which older California Cab to serve Saturday evening with those rare Strip Loins! Once you have decided you like these wines and the experience, the "skinny" is to purchase wines that have cellaring potential. You have a wealth of people to advise on this. winecurrent.com, the LCBO and other wine-related publications worth their salt will provide an icon or comment on wine that is worthy of your consideration for placing in your cellar. "Your cellar" has a nice ring to it, doesn't it?