I think the power increase from training should be judged based on what kind of training people do. I know that's more work for the GM and honestly, will probably cause some arguments, but it makes sense that someone who goes to train with Mr Popo in the time chamber would see more dividends than, say, Sam continuing to train with Kojiro.

Basically I want to see our efforts actually reflected in what kind of power increase we get.

As far as Saibamen go, it's a limited time solution. If Raditz used them here and then Nappa used them later, they would either be too strong now or too weak later on, since it makes sense that they would be the same strength both times; if I remember correctly their strength is based off of soil quality of something like that? At this point it doesn't seem like Raditz really needs the help, but he could still throw out some seeds in his next post with the justification of being annoyed having to fight so many people at once.

Then when Vegeta and Nappa show up rather than reuse Saibamen, maybe just have them bring a few jobbers from Frieza's army with them?