Ready for some market math? Decided to add together the current prices a few days ago. They've probably moved around a little, but here's what I have. Peruse at your pleasure! For the TL:DR crowd, the numbers as of a few days ago are currently:
3,311,312 Clintz is the current market price of every non-CR card in the game combined.
89,890,607 Clintz is the current market price of every non-CR card in the game combined.
Horrible Generalisation: If you were to try to earn the 93M for every card in the game only from winning matches, at a winrate off 100% at 7ish clintz per win, and a a time rate of 5 minutes per match, and not including any other factors, (various bonuses from the different modes, or how earned credits factor into it) it would take you....
Or about 106 years.
Maybe you'd prefer to buy the clintz, then?
Well, to get that figure, you'd be spending about...
or 3,141,000 Pounds
Read on if you want to see some of the finer figures.
Also, knowing when to buy cards is a huge factor, along with when to sell. You can buy some common cards for 300- while they're still in New Blood, but end up rising to 400+ after they leave. Some current staple cards which cost 10k+ used to cost 3k-.
I guess this all falls under investments though. :)
Not just investments. By having basic skills to pick good time to buy just one copy can make big difference on how much you have to "work" for your cards overall. If total value of all non-CR cards is roughly 3M and the half-yearly variance is +-20% in each card that means by hunting the cheaps is worth 600000 clintz and if you buy regardless of price you could potentially need to spend (=earn) 1.2M more clintz to get the cards when compared to cheapest (but more work-intensive) option.
The difficulty here is that some cards are stable, some cards are overpriced and some cards are underpriced. You'd need to skip the overpriced, get immediately the underpriced and hunt for the occasional good deals on stable cards. Underpriced cards will go up, overpriced come down by the time. Spotting these things are beneficial to everybody, not just investors.