Those minimap blips are not humongous, they are at the nominal and correct scale (1/64th of your vertical resolution). They only appear comparitively larger because your minimap is scaled down.
If you want "smaller" blips, you will have to use a replacement texture for them that actually uses fewer pixels, such as can be obtained using the BlipStick addon.
Please note that there is no API for replacing the new party/raid member blips. You will be stuck with those at their current size, color, and style until Blizzard decides to implement an API to change them.
Edit: You were right, too, and I was wrong. Your blips are really 20x20 pixels and not 16x16 pixels, like I claimed.
If that's the correct size, then they were incorrect prior to 3.1. The correct ones are about 2/3 of that size.
Yes, that is indeed the correct size for your screen resolution. That's the same size they have been since the earliest public beta version of WoW. The change implemented in patch 3.1 caused blips to appear "too small" at common screen resolutions and UI scales.
If you want your blips to be "too small' again like in 3.1(.0) and 3.1.1, the only way to achieve it is by using replacement textures, the same way we have been doing since patch 1.10.
Edit: You are right, I was wrong. Those blips DO appear to be too large. Using the original scaling algorithm, at 1600x1200 resolution, your blips should be 1200/64 = 18.75x18.75 pixels. Instead, they are 1600/64 = 25x25 pixels. This is an unexpected change from scaling based on the horizontal resolution instead of the vertical resolution, and will result in unexpectedly large blips especially for widescreen resolutions.
So chiming in again with my issue regarding being unable to hide the new mail notification button. I have it set to Never, but whenever I zone or log back in the mail icon will appear again and the only way to force it to hide is to go in, click on Never even though it is already selected, and save that but that will only last until I zone again.
The only addon I have that does anything to the mail button is Postal which hides it if all mail is read but has no function to show the mail button. I made a post in the Postal thread and this was the response I got:
Postal will only hide the mail icon if you leave your mailbox with no unread mail. Postal does not ever attempt to show the mail icon.
What really happens is that while Sexymap hides the mail icon initially, there is Blizzard code active in the default UI that shows it once in a while whenever you get new mail, and Sexymap doesn't respond to that.
I just moved to SexyMap from SimpleMiniMap. Love the mod.
Odd thing though, the actual position of the minimap on the screen doesn't appear to be saved to the Profile. I like to use profiles so that all my toons have the same experiences. All settings seem to get saved except the actual position of where the minimap is placed. (I like to put it near the bottom of the screen).