[scy]

...so I ended up running back and forth between rooms until I'd realized that I'd made a mistake or didn't push something far enough.

Haha ... this. This a lot. "I HAVE NO IDEA WHERE TO GO" for about 30 minutes until I realized I could push something in one more time.

Earlier on, it's much much harder because he's quicker than you and you don't have many artes. Because the cameo boss is Veigue, you know he's naturally weak against fire, so since I had Infernal Torrent already and included Malik in the party with a bunch of mid-tier fire spells, it was an interesting time. Since I wasn't far in the game and it isn't really recommended that you try it the first time you get to Warrior's Roost, I ended up wasting a bunch of Life Bottles. But in the end, it's worth it for the sword since you don't have to buy weapons for Asbel for a long time.

...

You can take items? Could've sworn the fight was with just the Grape Gels, Syrup Bottles, and Hourglass provided. This fight was frustrating since 500k HP on someone who just won't actually get combo'd. But, outside of the Mystic Arte, it was pretty much just a long fight.

Jeez. I feel like I'm always poor here. Is it better to just keep dualizing old weapons instead of buying new ones? That's my main money drainer.

How do I do this

Dualize stuff to sell, basically. I'm grinding the rest of the Stamps by buying 12 Rare Tunics -> Dualizing them to +3 or +4 -> Repeat. Each Tunic sells for around ~150k and it takes about 20 fights to dualize all 12 of them. I really should do weapons too.

Generally speaking, I do the following:
Wicked (Base Quality) + Rigid Shard -> Rigid Quality
Rigid + Rigid or Grand Shard -> Solemn Quality
Solemn + Barbed or Stuffy Shard -> Haughty Quality*
Haughty + Haughty Shard -> Poignant (OR + Sketchy Shard -> Perilous)

*If I don't have the next tier up, I'll use Wicked or Frosty Shards on the Solemn Quality to end up with Magical and I'll sell that since it has the best resell of the 7-letter Qualities. Magical + Gallant Shard -> Poignant works too I just never have the Gallant shards so I use Haughty typically.

For the demonstration, I'll use a [4] Shard since that's pretty common. As listed above, that gives you a +4 Weapon with a final value of:
= (Purchasing Price / 8) * (CurrentQualityResellMultiplier) * (1 + AllResellMultipliers) * (1.32 + ShardValue * .12)

Ending as Poignant:
= (27410 / 8) * (4.0) * (1 + .95 + 1.0 + 1.5 + 1.5) * (1.32 + 4 * .12)
= 3426.25 * 4.0 * (5.95) * (1.8)
= 146,781 Gald, * 125% for the Tempered Value so final resell is 183,476 Gald.

Ending as Perilous:
= (27410 / 8) * (3.0) * (1 + .95 + 1.0 + 1.5 + 2.0) * (1.32 + 4 * .12)
= 3426.25 * 3.0 * (6.45) * (1.8)
= 119,336 Gald, * 125% for the Tempered Value so final resell is 149,170 Gald.

Might be off by +/- 1 or 2 due to rounding.

Though, generally speaking, I don't follow it this strictly (since I don't have infinite counts on the shards involved) but I just remember the better valued Qualities to go through:
5-letter Qualities: Rigid (+95%) > Olden (+90%) > Sunny/Suave (+85%) > Noble (+70%) > Grand (+60%)
6-letter Qualities: Stuffy (+140%) > Solemn/Formal (+100%) > Barbed/Wicked/Frosty (+90%)
7-letter Qualities: Magical (+160%) > Haughty (+150%) > Untamed (+130%) > Gallant (+90%) > Sketchy (+30%) > Epochal (+10%)

And then I try to sell as an 8-letter Quality so the most important thing is the Resell Multiplier, not necessarily the Resell Inheritance. The Inheritance still matters, yes, but not that big of a deal so Dazzling wins out in the long run. Really, if I can't get Dazzling, Poignant, or Fabulous, I'll just stay as Magical or Haughty or something else:
8-letter Qualities: Dazzling (x5.0) > Poignant/Fabulous (x4.0) > Gracious (x3.5) > Perilous/Vigorous (x3.0).