Just my 2 cents, as I was once in your situation...trying to figure out if I wanted a point and shoot camera or the SLR.
I tried to capture some of the points you made in your post.
I am finding out myself just how incredibly difficult just my crappy macro work can be. With out a good lens you will be VERY disappointed with the results. I have 3 lenses for my Nikon D80: Nikon 18-55mm that came with the camera, a Tamron 28-300mm zoom, and I (my wife actually ordered it for me) just got a Vivitar 100mm macro lens (used off
ebay). I can tell you the difference between the Vivitar lens, the Nikon, and Tamron lenses are quite evident, (for 1 the 100mm is made for macro, so I can bring in subjects really close, and in better detail) but then again the lenses were designed for different applications. But on the flip side, if I were to slap a Nikon 60mm macro lens (which was suggested to me, though there is no way I can afford it right now) on the camera, it would blow the Vivitar out of the water....but that's the difference between a $150 lens off
ebay, and a $500 macro lens. Am I happy I got it, YES ofcourse! It has opened up a new area for me to experiment in, and see if spending the additional money on the other lens is something I can justify.
Can you still do
some macro work with the lens you get with the SLR? Probably, if you are talking flowers and stuff like that. But if you are looking at true macro (1:1 production) like you see with bugs that are really up close, then no it won't do that. As Overread was mentioning before, there are other lenses designed for that type of work, and those come at an added cost.
Point and shoots are really nice for the average everyday user capturing family photos, vacations, and that stuff. They are easier to carry around, and can take some great pictures. The drawback is you really loose more "specialized" type shooting situations where if you had an SLR you could just swap accessories.
Think of SLR's as more of a professional camera. You have tons of control at your finger tips, which can be even more frustrating when things don't turn out the way you want them to. There is a bit of a steeper learning curve with an SLR as well, working with my camera, I am still learning something new everyday. It can be quite a long process. The trade off though for having all that control, is more expensive accessories, steeper learning curve, and more frustration :mrgreen:.
As you already mentioned, lenses can be spendy. Specialized ones can be even worse. There are companies out there (Sigma and Tamron) that Overread mentioned, who offer pretty good lenses at less than a premium price. Probably every experienced person here will probably tell you, you will get what you pay for. Don't expect your $400 28-300mm zoom lens on macro mode to perform as well as a $850 105mm macro lens, because it just won't.
Personally if it were me, I would go with an SLR just because of the versatility you get with it. You're not limited to a fixed lens that comes with the camera. Down the road you will find something cool you want to do, and find out your point and shoot will require a teleconverter or some funky attachment that srews into your lens to make it work, or you just won't be able to do it at all. Not saying that you won't find the same thing with the SLR, (or that there won't be a time when you want some crazy $5000 lens

) but, I still think the versitility, control, and accessories of an SLR camera far outweigh the higher price tag, especially now when you can get a pretty respectable SLR with a lens for less than $500.
Just thought I would throw that in there....sorry for the long read

Hope you reach the decision that isn't right now...but right for you.