I don't think your friend needs to be able to play any country in the game in order to figure out if he likes CK2 or not.
We used to have these things called "demos" that would only let you play one level. Sometimes they would only give you one gun to shoot with...
Which might be why there's a "Download Demo" link on the Steam Store page or over at crusaderkings.com. I... haven't played it so I'm honestly clueless as to what it is (Paradox has earned my auto-buy).
There are a few ways to answer this.
1)Dollars per hour. It's a HIGHLY flawed argument, but it's not completely incorrect. I have about 1000 hours. I most certainly did not buy 100% of the DLC at full retail price, but I do own 100% of the DLC. So if you want to look at it this way, I pay 15 cents an hour. And I have fun.
2)Different DLC should be in different categories. There are 7 Expansion Packs. This is where most of the money goes. But, because Paradox is AWESOME, none of them are required. If you play as a traditional Western European Monarch for one or two hundred hours and you start thinking "Hrmm... I bet it might be fun to play as the Arabs or the Buddhists" then go ahead and spend 10 or 15 bucks or however much the one DLC you're looking at costs. These are old school expansion packs. No one should honestly have an issue with these. There are 21 graphics packs. These are truly just to add flavor to the game. There are 11 music packs. Honestly... these add a bit more flavor to the game than portraits and units. The music *IS* amazing, but trust me, at 1000 hours, it's nice to hear a change-up. Then there are a handful of other things. Sunset is basically a neat "what if" expansion pack, and then there's fun fluff like the character customization and the (very neat but not quite perfect) converter for us hardcore fans.
3)Tip Jar.
This is the way I look at it. There are SOOOOOOOOOO many practices that Paradox commits to that might cost them money, such as not REQUIRING that everyone have the same DLC. This might cost them money. But it causes me to love them even more. I'm okay paying a little bit more to ensure that they continue pumping out awesomeness. There's absolutely *NO ONE* else that's going to make these games. I'm not saying you should always put the full retail amount into the tip jar, but........ you should put a bit every now and then.
Plus... for those who are interested in the business side of it... buying the extra stuff really DOES help keep some of the people at Paradox employed. PLEASE correct me if I'm wrong on this. Please. But, to my understanding, everything is done in-house. The musicians/programmers who are the ones making the musical DLC are Paradox people (same goes for the graphics people, but I'm using music people as the current example). They release a full game every year and a half or so. Trust me, there isn't a year and change of work in the base game for those employees. Normal developers let their employees go all the time, or they hire out independent people from the outside all the time. This isn't a bad practice mind you. Jeremy Soule, for example, makes amazing music. But I'm pretty sure Paradox (the Dev Studio, not the publishing company) doesn't have the capability to have that kind of turnover in team. So... when I buy musical DLC... I'm helping to ensure that the musicians stay on board and are there for the next game, ensuring consistent quality. Again, please correct me if I'm wrong on that particular part.
And c'mon... how much do people normally pay for music when they buy retail? Averages around a buck, right? Let's look at a random music DLC. 99 cents for Songs of Byzantium which includes three tracks that add up to 11 minutes. Now... I know most of us aren't loading these tracks up on our mp3 players to jam to on the way to work, but still... it's a good value! I sometimes think back to my old JRPG days on my Nintendo as a kid and how the music just got horribly monotonous, no matter how good it was. With the DLC, you can at least get a nice variety.
Anywayz... those are the three points. I *may* have gotten a bit long-winded, but I think I got just essence conveyed. Just tell them to get the demo (20 years, no save, full-featured otherwise) and then explain all this to them.
Good times.