Answers to your questions:
1. Realistically what would be considered as past it for a Dubai jeep?
Nothing really, i have seen 94 model jeep too. So actual catch will be answered in next question.
2. I know a 04/05 Pathfinder will probably go 750,000kms if looked after well enough...what about the Wrangler?
Indeed if well looked after jeeps easily touches 200k - 300k on single engine. Make sure buy from someone who has not driven or rather abused in desert every week. As wrangler is good for offroad, so people tend to abuse it and sell it fast before it turns lemon. Buy low milage wrangler under or close to 100k with first 3 years maintained with dealer, even if you pay extra 10% over other models with no service history and clocking 200k its well worth. Trust me.
3. With a budget of 30,000aed what could i expect to get?
This is very good time (peak summer) to buy Jeep, you will understand why after you make a buy. lololol.
4. Are there any common issues that i should be aware of?
Get the axle and differential check THOROUGHLY as these both are the weakest point of any wrangler to my knowledge.