We've done IVF twice. The doctor in question (Geeta Nargund at Create Health) said she thought we had an excellent chance of success, based on test results etc. From what I hear, she is a straight talking woman and would not have said this unless she honestly believed it was true - have come across a few different stories of her making it quite clear to people that she thought the chances were low.
The only downside is my age. I have the right levels of AMH, FSH, LH etc, in fact wonderful levels for my age (41) - she said you would typically see similar test results in someone ten or even fifteen years younger than me. I ovulate naturally. Antral follicle count has been good every time it has been taken, ranging from 9 to 15 I think. DH has had sperm analysis results ranging from very decent to excellent. I've had laparoscopies, HSGs, all the investigations you can think of (bar the NK cells business, which I'm now considering as an option).
There is absolutely no medical reason yet found why we should not conceive apart from my age.
I've had two natural pregnancies - one resulting in DD and one MMC which was discovered at the 12 week scan, sadly. But it took a LOOOOONG time to achieve each of those - two years and three years respectively of really trying.
So I am a bit stumped. I wonder whether there is really any point in spending another £5000 on no baby. Although as my aunt pointed out, £5000 on no baby is cheaper than actually having one! 
Would you try again in my shoes? I am starting to wonder if the path to happiness is really just accepting my (luckier than many) lot. After all, I have a child. I love her to bits and I am very lucky in so many ways. But I would like another, I really would. I'm just not sure it justifies spending another £5000!