I know changing the scale on the fly works. This does scale up POI icons and other things which can look pretty bad at a very large scale though. I use the following extremely rudimentary code in my own UI which simply scales it straight up to 2x, 3x, etc. size for help when herbing or mining by using Alt+Mousewheel.
Lua Code:
local function onMouseWheel(self, dir)
if IsAltKeyDown() then
if (dir < 0) then
local newscale = Minimap:GetScale() - 1
if (newscale < 1.5) then
newscale = 1
end
Minimap:SetScale(newscale)
else
local newscale = Minimap:GetScale() + 1
Minimap:SetScale(newscale)
end
else
if (dir > 0) then
MinimapZoomIn:Click()
else
MinimapZoomOut:Click()
end
end
end
--
Minimap:EnableMouseWheel()
Minimap:SetScript('OnMouseWheel', onMouseWheel)
Obviously if you wanted it to have smooth transitions or draggable handles or smaller step sizes you'd need to do some more work there.