SP keycaps are very beautiful. But also it's thinkness is too low and durability is disappointing.
I think it is decoration for keyboard.
SP makes a few different profiles. I agree with you about DCS profile, but SA profile is thick and solid and awesome

Semi-matte keys shine quite quickly (couple of months of hard use), but they look and feel great great, even when shiny. In fact the shine suits the style of keycap and I feel they're very retro. The shine adds some character, IMHO.
My favourite keycaps are the Penumbra set.
If you REALLY don't like shine, get some textured dyesub PBT caps. All ABS caps will eventually shine. Actually, even the most textured PBT caps will eventually shine, but it takes a lot longer to wear down.
I have learnt to embrace the shine, but only buy SA profile from SP (never DCS or DSA). I also like GMK doubleshots and those new JTK caps look good.