Lived there for 3 years and never bought anything other than duty free. The allowances are huge. We stocked up every pass through. Visiting relatives had a standing order. We never visited the famous hole in the wall but have friends that were regulars there. Cheap booze, no tax.
at emirates road take exit 103 and just follow dreamland aquapark or barracuda signs. it's right after the plane just before the petrol station. on the road back I'd suggest to take dubai by pass road (E611) before you reach sharjah, a little longer to get back but no traffic etc.
getting lost once or twice is almost certain [: .