there are many one time bonuses which will far outshine your stat bonus...
Actually, a good one that I can think of is the Fighter's Combat Superiority bonus. Let's look at the point buy costs to see what I mean...
To buy the following you will pay:
14 - 5 points
16 - 9 points
18 - 16 points
Now, looking at a Fighter he gets a bonus to his AoO's from his Wis mod. If you buy an 18 in Strength and then bump that to 20, you get the extra +1 to your attack roll for a total of +5 to attack rolls...but at the cost of an additional 5 points over the cost of a 16. Your bonus if you're using a non-sword weapon would be a total of +8 (+5 for abil mod, +2 for prof, +1 for weapon talent).
But now you have no Wisdom bonus, so you're a big threat in terms of AoO's. Essentially, you have the same chance to hit if an enemy moves past you as if you were attacking them directly, which is a +8. However, that attack will be a melee basic, rather than an At-Will.
Now, if you point buy a 16 for a cost of 9 points and then bump it up to an 18 in Strength for a total of +4 to your attack rolls. This comes out to a +7 to attack rolls (+4 for abil mod, +2 for prof, +1 for weapon talent). The 18 only cost you 9 points though, rather than 16, which means you have an extra 5 points to play with. With that, you can buy a 14 in Wis score, which for a Dragonborn doesn't have a racial mod and would've been a 10.
This means that now you get a +2 to AoO's on top of your normal modifiers, so that's a total of +9. You're now more likely to hit your AoO's than your normal attacks, which means it's now riskier for a monster to run past you than it is to stand and fight you directly. You'll do more damage with your At-Wills of course, but you'll be less likely to land them.
What does all this mean though? Basically, as a Fighter, it means you just became more sticky. Enemies will be less likely to try to get past you because of your AoO bonus, and thus you can keep away from the squishies. Even if they do decide to take their chances and get past you though, you have an extra +1 to your AoO's versus the 20 Strength build, which means you're more likely to hit on your AoO's than the 20 Strength build. And if you do manage to hit them, then you will interrupt their movement and
still keep the enemy out of your back row.
The net gain here is that you're doing a better job of being a "Defender" and using your class abilities. This is why secondary and tertiary scores can be important. From this point on in leveling you can pretty much ignore your Wisdom score and just keep that little +2 (Eventually a +3 because of the tier ability increases that do +1 to all ability scores) around to give you that extra bump...essentially it's like you have combat advantage any time someone tries to slip by. With the 20 Strength build you might end up not pumping Strength during some levels in order to increase your other ability scores. Or even if it's not Strength, you second point per level would be spread pretty thin between other potential scores like Constitution and Dexterity.