Yeah, Erebor has huge strategic value, for several reasons.

First because a mountain fortress is an inherently defensible position (to say nothing of one built by Dwarves, who are canonically the best builders in Middle Earth).

Second, it's the Lonely Mountain - it's the only one for hundreds of miles. Combined with the above and it will serve as a tremendous castle from which to project power, just as traditional castles did. No force could be sufficiently omnipresent to exert its influence all over the lands held by their leader, so you built a castle and have a safe base to sally out from as needed.

Third, Smaug's been hoarding unimaginable wealth within it for two centuries. I mean, there's enough gold in there to take a Scrooge McDuck-style swim in, to say nothing of the special treasures like objects made of mithril (remember that the mail vest Bilbo gets is worth more than the entire Shire) and the Arkenstone. Quite aside from any value in the fortress itself, it's totally worth a raid, either for personal wealth or to fund your armies for an extraordinary period of time.