Granblue Fantasy: Versus with 90 % discount on Steam

You have the right points if you want to get into the game and play online, but for $2, this version offers pretty good single player content and you can play with your friends if they also buy it. Rather than the $60 and find out you don't want to invest that much time in this particular title (specially if you already play/main other fighitng games).

It actually is: vale=it is worth / ne vale la pena=it's not worth the effort

Unfortunately, I don't have a copy of this myself, but here's what I've picked up on the game, for initial consideration:

Much like with Mortal Kombat's Shaolin Monks spin-off game, or Street Fighter EX3, this is a side-scrolling beat em up style mode overlayed onto a fighting game. The DLC characters appear to be additions, rather than expansions to the gameplay, in the same way normal fighting game or beat em up roster additions would function.

So in that sense, the only characters you'd need are ones you especially favor- there's no gameplay reason to necessitate having additional characters (as in, there's no linked stage unlocks, no additional loot types to drop, no party composition concerns, no team combo mechanics, etc, that other fighting or RPG games sometimes have to encourage additional DLC characters.)

Likewise, apparently the characters are archetyped, much as most Soul Calibur characters are (eg, Heavy, Light, etc or, in Soul Calibur, Spear, Sword, Etc), so in theory DLC characters shouldn't be as dramatically different in tone as, say, a Marvel vs Capcom or a [non-swordsman 🙄] Smash Bros. character might be.

That said, some of the DLC character are supposed to have fairly distinctive movesets beyond their archetype (though near as I can tell, none are pulling a Voldo, so they're probably not TOO distinctive), so it may be worth looking at specific purchases based on your playstyle (eg, I've heard that one is supposed to specialize in grappling moves, and it's worth noting that the story mode's boss antagonists can apparently be unlocked as playable characters through DLCs).

On the other hand, as the RPG Mode progresses you move from being forced to play as the default character (gender swap available at any time) to unlocking new characters to upgrade and play with through the mode. So there's already a versatility benefit to having more characters available, unless you're the type to stick to a specific character in a fighting game or brawler without losing interest.

More importantly, though, the characters [both default and DLC] apparently come with their own story missions (browsing through the Steam store pages, it looks as though 2 quests per DLC character is the standard), so you may be missing some side-lore and expanded gametime by not having the DLC characters (it looks like there's 50 "episodes" in the core narrative, so given the number of DLC characters, you might be missing out on like half the game without them).

TL;DR version:
From a fighting game perspective you'll probably want to confirm none of the individual DLC characters especially appeals to you.
From an RPG perspective, you'll want to get them all if you're a narrative completionist- for the bonus side missions they unlock- but won't hurt out otherwise if you don't.

P.S. Color palettes can puportedly be purchased through in-game currency after completing the RPG Mode, so the DLCs to unlock them are completely non-essential. Likewise, stage DLCs shouldn't have any connection to the RPG Mode, and should also be ignorable.

Likwise, if you missed it in the earlier comments, the following are worth noting:
1. Your progress should be able to be imported into the remake, allowing you to smoothly move from this $2 version to a more complete version.
2. The remake is not only going to integrate DLC characters, but will expand the story content. Initial story content will apparently be provided in a more condensed form, however, so there's still some potential benefit to getting the original release. If you're looking for a complete narrative experience, you'll nevertheless eventually need to get the remake.