I do think it's really interesting that Dracula genuinely seems to enjoy talking to Jonathan Harker. Yes, partly he's trying to learn valuable information from him about English society, customs and laws etc. And yes he wants to practice his English with a native speaker - though clearly Jonathan was not his only source of English lessons. But it goes beyond that. Like when he's talking about the history of his family (well, actually events he mostly lived through but obviously he can't admit that) he gets really animated and just seems excited to have someone to monologue to. After all, he doesn't have that many people to talk to. I don't think in general his meals get much of a chance for a chat. Who knows how long it's been since he's really interacted with anyone (aside from the other vampires in the castle).
It's not a wholesome interaction of course. Part of the enjoyment he gets from their interactions is derived from the way he toys with Jonathan. But it does definitely go beyond simple necessity. He really goes out of his way to spend time with Jonathan, often speaking with him all night - i.e. the whole time that he gets to be awake. And he also goes out of his way to protect him from the vampire women in the castle, even after he's outlived his usefulness. And he becomes increasingly possessive of him - "this man belongs to me" and "tonight is mine" are certainly telling. It seems that initially Jonathan was just going to be fed to the vampire women right away, but then Dracula changed his mind and decided he got first dibs, something that wasn't initially in the cards.
I think this possessive fascination with Jonathan and the way he comes to find their interactions genuinely enjoyable are why Jonathan gets to stay alive so long. Even going poking around in Dracula's crypt the first time isn't enough to get him immediately killed that night. I wonder if in his own way he also was drawn to the "quiet dignity" that Mina mentions is one of her favorite features about Jonathan. Even in the face of fear and despair he stubbornly clings on. Dracula probably finds this makes Jonathan more entertaining and exciting to toy with than most victims, and may also feel a grudging sense of respect for him (although he still views him as an inferior).