i don't know about minnowbooster, never tried it but the most "passive ROI" schemes i see take a loong time lol ... 

its a bit dependent on the price too, at the moment 100sp is basically nothing but a little bandwidth , the voteworth of that should be about ...

roughly at time of writing :

cat@cerebro:~/Documents/steemUX/commands$ ./wurdamoney.sh0 rudyardcatling

.05613426154679823966

which comes down to , euhm ...

0,005894737 for about 100sp ... 

which means free account plankton despair lol , if i look at the numbers the vote was about 0.061 over 250sp ago so its really bad with the price war and the assault

you get about ten votes a day at 100/100 ... make that nine more like because its not every two hours so 

daily your 100sp is worth  what ? 0.045 ? that is if you vote nine times on yourself on a post or comment that passes dust treshold

so you can take it from there, how much do you get for delegating 100sp ? or 200 is just x2 and so on , 

that should give you a relative setting

(but only at the moment of writing ofcourse) im not gonna name or advise for or against certain systems or bots that promise daily returns , you should check for yourself