Its hard to get lvl1 gold mods... And much much hard to get a gold mod with good potential (just speed in a secondary)... And infinitely more hard to upgrade that mod and get good results (see sped increase over +15).
So dont worry a lot about gold mods... U usually will get better mods starting from blue and purple mods (even from green xD).
A green mod with +5 speed will finish at lvl 15 with +8 or +9 for sure... And a gold mod with +5 can finish at 15 with just +5 speed and +30 defense (a total waste xD)
All u have to worry about mods is to lvl up only those ones with speed at lvl 1 and u will do fine! Speed is everyting in this game xD