I also believe the $10 pack that's dia + some storage upgrades has a pretty decent value?
This was the last 1-time pack I bought. The value isn't great, but if Dream Summon rolls around and you have Resource Pack active but don't have 1200 Dia, it can get you there.
I would recommend the other 1-time packs that I didn't exclude [Story Pack (Normal) and Upgrade Pack (Adventurers), as well as every single item under the "This Week" tab] before getting the Storage Pack, though I suppose most of them have depreciated in value over time. Storage space rarely matters unless you hoard things you'll never use.
Regarding the Welcome Pack:
Naveed: Bad. His kit functionally doesn't work even if given time to power up, Marth ate his lunch and even Karl/Euden and the other dozen Fire Swords are comparable.
Mikoto: Overrated because of launch players and High Midgardsormr runs. Still solid, but most likely isn't your best Fire DPS these days.
Ezelith: Newbie-friendly, but awful long term. She's the martyr of the launch banner.
Xander: Top-Tier if Gala Cleo doesn't exist. A kit that does exactly what a Sword should do, and even has a ramping Skill 1 that scales with good teammates.
Xainfried: Doesn't exist. Did you mean Elisanne? Fjorm? Cibella? Jakob?
Lily: A discount Maribelle with Freeze which trivializes a lot of content. She's almost never #1 optimal, but always decent and a great speedrunner for easy content.
Hawk: Elias deals similar damage. If this isn't clear, Elias is pretty awful.
Louise: Passable leaning weak, but she has much to gain from the upcoming patch to status effects. With more Poison procs and Pazuzu, she has pretty decent DPS and an underrated Co-Ability.
Maribelle: She's always been strong, and is one of few units who has received a nerf in the form of non-stackable Defense Down on her Skill 1. She was viable for the upcoming Astral Raid boss, which is Fire-typed. Yeah.
Julietta: Light Axes are bad. While Julietta doesn't top the damage charts, she's not too far behind and has a hell of a lot more room for error on her HP. She's a good specialist for Facility Events, as the AI prefers super armor and the Axe weapon range does better than Lance as far as super armor weapons go.
Lucretia: The worst Light Wand unless you've got a very niche Energy synergy going on. Remember that stacks of Energy only count as one buff total. As Wands for Light content go, Gala Cleo>>>Xiao Lei>Amane=Lucretia.
Hildegarde: We just got Shadow Verica, but as generic healers for Solo/Auto content go, Hildegarde is still #1. She's not really suitable for long duration content, but she doesn't have much competition there either.
Nefaria: The worst of two bad Shadow Bows, and I have a 50 Mana Circle Norwin and 40 Mana Circle Nefaria.
Not worth investing: ~6
Passable: ~2-4
Great: ~4-5