One of the things that always amuses me about this board is that relationship threads will always go on for at least 8 pages. This is not a critisism of the OP, but merely an observation. Now i suppose i should say something on topic...
In terms of "aqquring" a relationship i'm not very useful. I was very lucky with my first and only-so-far relationship where i barely had to lift a finger to go out with her- she did all the work. Ringing me, asking me out etc. (If only all girls were like that?) So i can hardly say if the "effort investment" is worth it, but relationships themselves, when they work, are brilliant, but when they are not working, are horrific, and i've experienced both sides to it, it's an investment not to be taken lightly.
When you are in a relationship, i suppose a good way to decide wherever you should end it or not is when your "effort investments" are not paying back with the profit which comes in the form of happiness one gets from a healthy relationship. When i found my effort investments were not paying off in my previous relationship, i wasn't happy for these reasons, and thus i was forced to end the relationship.
As for aqquring one, some people obviously find it easier than others. So starting with some advise i recall that girls have said, they like guy's to be outgoing and confidant, so presumably the male is meant to make the first moves and whatnot. One of my friends loves doing this, and good for him i suppose, he's had countless relationships. But, i suppose not all of us can be, even if we tried to be, outgoing and confident. I certainly couldn't, and as i've matured and come to "know myself", i've... become more passive when it comes to aqquring relationships. I don't fancy certain members of the opposite sex with the intensity that i did in high school, i'm more analyitical of their personality and interests, and only if i can muster enough passion and if the woman in question reasonably passes my analysis can i see myself putting the effort into attempting to aqqure a relationship. I suppose i'll have to someday, as The Gentemen said, you needs kids to add to your pension fund.
I think, in a nutshell, the problem for a lot of people is finding the right person and most ideal situation in which you can work on aqquring a relationship with them. This set of condition arises only with luck. Sure, its advisable you load the dice by having an active and diverse social life, but even that won't guarantee you'll roll a D20 or a double six or whatever's your jackpot number, that's what you need is luck to meet that right person in the right kind of situation.