Ok, it's my second runthrough and I've unlocked the grade upgrade bonus in the grade shop. I have the devil arms and Lloyd is rocking about 2,750 to 3,000 points of damage per hit. I haven't noticed any increase in a long time so maybe it hit a damage cap with him.
I've got my three other characters on standby so the aren't doing anything. This means they shouldn't use any tp during the fighting. I've got a heal bracelet on Lloyd so he hopefully finishes the fight with full hp. I just entered the Tower of Salvation following the Flanoir doctor event, and I am fighting with Lloyd's normal attacks so I am not using any tp.
Smashing the normal plant and angel enemies is getting me 10 grade every battle as long as everyone's tp stays full! Craziness!!!
Keeping the streak going is actually a bit tricky, and as the number of characters in your party decreases, the amount of available grade that can be earned decreases. However, I found a really easy spot to farm right before the Lloyd/Genis event. There are two angels in the hallway which can give you a fight with an angel swordwoman, an angel spearman, or an angel commander. Each of these can be killed by devil arms Lloyd in one combo. I use the forward-x, neutral-x, neutral-x button combo myself since Lloyd does a spin that gives an extra hit.
Anyway, the swordwoman and spearman will give you 3.60 grade if you run right up and kill them fast since you get a speed kill bonus as well as a no damage bonus. The commander gives you 8.00 grade for the same. You can then turn around, zone back and forth through the warp and kill them over again. It's a very fast farming method. I stayed in the tower until I had about 120 more encounters on the battle counter than I went in with and came out with 800 more grade.
I went into Torrent Forest next and found out that this method works much the same there, though the screaming plant women are trickier, and the green pepper monsters knock you down a lot. Putting a blue sephira on a Hold Position party member and zoning on the gold dragon earns buttloads of gold and grade at the same time, though the grade isn't quite as quickly earned there. A good solo-Lloyd kill on the dragon gets you about 9.00 grade on average but the zoning takes longer.
Just to clarify, you get a good grade bonus for finishing with all hp, all tp, speed killing, killing more than one enemy with one attack, taking no damage, and killing the next enemy quickly after killing the current one. This goes for all party members, so this method focuses on keeping everyone at max hp, max tp, and hopefully including some speed and no damage bonuses. The heal bracelet really contributes to your grade collection.
***Note: when a character level ups, he/she won't be at max hp any more, so remember to heal using a non-party healer. The slight bit of missing hp really saps your grade farming.
Well I ended my first run with only 1500 grade so even with 2x grade bought farming another 8500 to buy out the grade shops takes so long I'd rather play the game for those +70 hours by beating it 7 to 10 times.
Over farming this 8500 grade on a first or 2nd full run of the game.
Well, everyone has their own way of playing the game.
Here is an interesting additional note. I was back in Torrent Forest wiping out the gold dragons when the grade I was earning suddenly got cut in half. It seems there is a bonus on grade earned based on your level or something, so once you level up enough the method isn't as profitable. So if you want to cash in on the biggest amounts of grade, it's best to grind in these areas until you get up around level 75 or so and the grade bonus drops. That's what I think happened, anyway.
For the record, I beat Abyssion at level 57 and went into the Tower of Salvation in the early 60s.
I'm getting around 1600-1700 grade on my first run so I'll have around 2600 or 2700 going into the second run which will get most of the important stuff. I'll have to go without the experience multipliers or gald transfer though, but after that I can start getting them with each run. Just a few hundred more grade and I'll be ready.
So it's a bit of a middle ground between farming it all and playing the game for it.
If there is a low level bonus the way there seems to be on my own run so far, then that provides the good incentive for a little farming. Spend some extra time in those areas if you are still low enough levels, collect extreme amounts of grade until you level up and then move on. That keeps you on the middle ground and let's you milk the most without excessive grinding or over-leveling. You could finish a regular game with an extra thousand grade or so.