Entertainment value is what it comes down to I think. Lets Plays aren't my favorite type of video to do, and I didn't start a lets play series until a few weeks ago. However, people really seem to enjoy them. The type of video I normally make is more of a highlight reel. But I think the question your asking is it worth spending money to be able to record game play.
If you're like me, then hell yeah it is. Before I had one view or even uploaded a video to YouTube, I spent countless hours in my video vault for Call of Duty. I found that I absolutely loved editing game play. It didn't matter that at first it was only my roommate seeing my work, it was that I had fun creating it.
It has eventually become a job for me. Money is an issue now, but if I did it for the money, I would have quit already. The game I post on now happened by accident. I started playing a mobile game, starting spending a lot on said mobile game, then starting posting videos on it. I don't regret a dime I've spent, but it was all money I spent to entertain myself.
If you have fun watching your own game play over, editing it, commentating for it, then go spend the money for a PVR.