No other card will bring You any improvements at 2D (something on which
all cards of the last ~5 years are equally good

Not the case at all.

There IS a strong variance between the 2D capabilities of chipsets made by
players other than ATI and NVidia (like Via, Sys, Intel etc...) over the
past 5 years. To be accurate you'd have to say (something on which all
NVidia, ATI, and Matrox cards of the last ...say 3 years... are equally
good)

Tony