The randomly generated value is used in two ways.
First off, it is the ONLY factor affecting flavor. Amazing/Great/Terrible/etc. is all dependent on this flavor value. It takes the string "Apple Apple Grape Grape etc." (I'm not sure exactly on the names/formating). It hashes this value. It then converts the hashed value to an integer and uses this as the seed for the Randomizer. It then pulls out 3 floats from the Randomizer, and averages them. If the number is less than .5, it multiplies it by two. If the number is above .5, it subtracts .5 and then multiplies by 2. It then adds the median combo multiplier (fixed value set internally but modifiable) to the product of (the Max combo multipler minus the median combo multiplier) and the value computed above. It then compares this to it's internal threshold levels of .5, 1.2, 2.5 and 4 (these are individually modifiable as well). Anything below .5 is terrible, .5-1.1999 is poor, 1.2-2.4999 is well, etc.
Now this value is also used as a multiplier (along with several other multipliers including whether you have flavorful feet, upgrades to nectar maker, your skill level, etc.) to determine the value of the bottle. This does explain why there's variance within the Terrible, Great, Amazing, etc. ranges. It's not using Amazing as a multiplier. It's using the value determined above as a multiplier. Further explanation in P.P.S.
Hope this helps.
P.S. I'm a little burnt out, so I'm not going to put a how-to guide on how to access all this information. Do a google search on reflector (the app I'm using to look at files), and "sims 3" and that should get you started. You'll also have to unpack some of the game files which you can do with s3pe. When you get all that done, the info above is in "Sims3.Gameplay.Objects.HobbiesSkills.NectarMaker.NectarFinishTask".
P.P.S. Code for determining value:
float baseValue = ((((((num * num2) * num4) * this.mFlavorMultiplier) * num7) * kQualityLevelMultiplier[((int) num5) - 1]) * this.mMultiplierFromFeet) * makeStyleValueModifier;
num = sum of the internal nectar values associated with all ingredients (for example, apple is 5, life fruit is 22 - this is regardless of quality)
num2 = Random Multiplier (although it's constrained to a range that's set by other constants)
num4 = skill multiplier
FlavorMultiplier = Whether the nectar maker is flavor upgraded (1 if not, more if it is)
num7 = the long "taste" multiplier i talked about at beginning of post
QualityLevelMultiplier & num5 = Multiplier based on quality of produce
MultiplierFromFeet = Flavorful feet multiplier (1 if regular feet, more if sim is challenged [pun intended])
MakeStyleModifier = Multiplier based on the kind of nectar you made (extended, concentrated, mass produce, etc.)
