Perhaps an add-on can be made that allows you to configure what levels mean what (such as making Yield 2 mean 1-2 produce, Yield 3 means 2-3 produce, etc), make seed drops from grass have random levels (configurable, including what maximums and minimums are dropped), and maybe increase the maximum level past 10, as long as the configuration doesn't create some nonsense like "130% resistant to weeds" (Where the default level 10 is 100% resistant). This add-on could also (configurable) handle increasing the range of cross-crops concerning cross-breeds (Such as within 1-2 tiles orthogonally (Taxicab geometry); or within 1 tile including diagonals) and breeding of trees/saplings (also configurable, cross-breed range configurable separate from crops and is defaulted to 3-5 orthogonally, base block of the tree becomes a special "crop log" block that just yields a log when broken but acts as a crop as far as breeding goes).
One thing you could do with the theoretical add-on is make it so that the maximum level is 3; level 1/1/1 is equivalent to the normal 1/1/1, 2/2/2 is equivalent to 4/4/4, and 3/3/3 is equivalent to 8/8/8. And don't enable tree-breeding/growing. Increase weed-growth range to 1-diagonal and leave crops at 1-orthagonal.
Also, quick question. If a custom crop has two products listed, does that mean it has a chance of being either or does it mean it will always produce both? Is that what the weight stat is for when defining products?