I'm reading an old book (こころ by 夏目漱石) and there's an unfamiliar grammatical phrasing that has fallen out of fashion and/or that he was rather fond of: ~だの~だの, e.g.:
。。。イサベラ何何の墓だの、神僕ロギンの墓だのというかたわらに。。。
The dictionary I use suggests it's similar to など/とか in meaning&usage. Are there any important differences?
There indeed exists a fairly important difference between 「～～だの～～だの」 and the other juxtaposition structures such as 「～～とか～～とか」、「～～や～～など」、「～～とか～～など」, etc.
The difference is that 「～～だの～～だの」 would generally imply the speaker's negative feelings about the items being juxtaposed all by itself even without using further negative words around it.
The other forms of juxtaposition do not carry either a positive or negative connotation all by themselves. That value judgement would need to be expressed with other wordings around them.
To put it in the simplest terms possible, you are complaining about something 95% of the time you use 「～～だの～～だの」.
By "negative feelings" in this case, I am referring to juxtaposing:
1) worthless items or statements by the speaker's judgement (I did not mention juxtaposing statements above but it is a feature of the だのだの form.)
2) unrealistic and/or unsubstantial items by the speaker's judgement
In OP's example, the 「何何」 part of 「イサベラ何何の墓だの」 alone already expresses the speaker's negative feeling, IMHO.