Tough one. I think you need to look at a few factors, but the three key ones are:
1. Where is the market now?
2. Where do you see the market going?
3. What will it cost you to own?
E30 325i.
A quick glance at Gumtree doesn't give much away, but the global market sites show that they've levelled off around $16 000/R230 000 for the really nice ones. They've been hanging around there for the last 3-6 months.
Cost of Ownership is a tougher one. Insurance in SA will certainly hurt, with the known desire for these cars among those who don't want to pay for them. I don't have any experience regarding what they cost to run, but if you want to make money on it you'll need to buy better parts than some of the generics on sale from some retailers. I can't see that being cheap.
So applying our questions:
1. Stable at R230 000 for a nice one.
2. This is more subjective, but I can't see them going up very much. Nice ones might go up a little bit, but a 325i is not a R300 000 driving experience or particularly unique & interesting. I think this will reflect in the relative lack of growth for them.
3. As much as any nice older car with a high insurance premium. I think the cost of ownership will outstrip any growth you might see in the sales price.
The E36 M3
This one is far more interesting. The local market has cars being advertised from R140 000 - R400 000. I'm not sure what they're actually selling at, but in this economy, I think the selling prices might be far less. So that's something.
Where might the market go? Well, late 1990s BMWs are the current "hot" trend. E39 M5, E46 M3, M Coupe are all climbing in value. And as they become more valuable, the associated models tend to enjoy some of that growth, so things look good for the E36 M3.
The other factor I can see in the E36s favour is the wet-blanket M3 that the Americans got. (Theirs came out with 179Kw vs the 210kW/239kW the rest of the world got). As such, American collectors are showing interest in the more powerful version and joy of joys, from 2020, the 239kW 3.2 E36 M3 will be eligible for import into the United States. European hot hatches have gained value when they were importable, and JDM classics have enjoyed similar growth. So there is an opportunity here.
Then, ownership cost. M3s come in 2 versions: Ones that were R400k and have been beaten and abused to a value of R140k and ones that were loved and nurtured. Each comes with their own cost of ownership profile. On the beaters, you're spending money to make them just work. But the unicorns need love, care and good parts to maintain their value.
Running the three questions:
1. The market is all over. But unicorns seem to be advertising for north of R300k.
2. I foresee this growing. A mixture of the American market opening up and the general drift from the E46 and E39s growth means great ones will pick up in value. I don't think you'll see the crazy numbers we've seen for E46 M3s but there will be growth.
3. Incredibly dependant on the one you get. If its a turkey, expect it steal your wallet and run off with it. If it's a good one, parts will be a little pricey but nothing dramatic. One of the worst cases of "it depends"
So to answer your question:
E36 M3, but be careful about the one you buy.
Please feel free to disagree if you think my process is wrong. Good luck!