I to won't look at spoilers or any of the info that will tell, I want to do this all on my own. I use the blank sheets to track what I find and it is working well. So I really don't know what to keep or to throw away, just have a few suggestions.
There are 4 things that can't be cross polinated, you either have to buy them or mutate them. I won't post them as that to me would be a spoiler, but I have found this so after doing a bunch of crosses and discovering on my spread sheets, that certain ones, I am not coming up with at all. So I don't get rid of those seeds. I don't get rid of a Tier 4 that I either bought, mutated or cross polinated, until I have been able to cross polinate it by using other Tier 4 and other Tiers(hope that makes sense to you).
But really don't worry to much about throwing any other seeds away, if you keep track of how to make them, by using the blank spreadsheets, you can always make it again if you need it later.