Honestly, if you’re only using Venusaur and growlithe (which I’m sure you’re not doing) then YES it’s worth it. The two will probably reach lvl. 50 at the 6th or 7th gym, and if you’re not willing for the miss chance with Fire Blast, then I would get it flamethrower. But also, if you’re not using just two Pokémon, it’ll take a VERY long time to get it to 50, due to grinding and the levels of the Pokémon in Red (both trainers AND wild Pokémon.) I’m also sure you don’t want to be grinding for a playthrough that’s for fun, but that’s just me. Another thing to think of is that fire types aren’t the best in Kanto, because although there is an abundance of grass and bug types, and the gym leader Erika, it’s best to just get a Poison or ice type. Also, with Lorelei you might say, it’s good against some of her Pokémon, BUT in gen 1, Ice attacks are neutral against Fire Pokémon, and it, even as an arcanine might die from an ice punch from Jynx or blizzard from lapras. These are all viable options, just take the one you want to do the most, and I honestly recommend all of these options. If you have any further questions say so In the comments and I’ll answer them to the best of my ability.