I get broody too and my baby is only 15 mths old. Having 2 has been alot easier than just one...it's hard to pinpoint why, even though you're stretched more in time and energy terms. Hugely complicated I guess...along the lines of...
a) you know what you're doing with no. 2 and there's a funny satisfaction in knowing which corners you can cut and which you can't. You've pretty much faced it all before and don't worry as much I think
b)dd1 amuses and entertains dd2 (4 year age gap) - well, at least until 2 weeks ago when suddenly they've started fighting (ds1 asserting herself)
c)all the money I foolishly spent on things for dd1 has been put to good use for dd2 (cot, toys, clothes, etc). In fact, I've hardly spent anything on dd2 - might well change in the future though when she cottons on to only having things passed down.
d) I'm enjoying being with dd2 as a baby more - again, probably because I'm so much more laid back. She's also easier than dd1 was (down to me? her personality? who knows??)
I think the best thing is to think...if I didn't, then when it's too late, do I think I would regret it?
We thought dd1 was going to be an only child - and before the second came along, she was really sociable with other kids, made friends easily - so I don't think only children are necessarily more lonely or socially inept in any way. She would have been fine as an only child. Equally, she's fine being one of two - she'll turn out differently I expect - through having a sibling - but no better or worse than if she hadn't.