wear the watch and pack the box in luggage. If kiasu, mail the receipts back to home address. i don't know anyone that's gotten checked and "taxed" yet based on buying for personal use.
the law is crafted as a catch-all more to target those running a business that are shipping in goods in bulk to avoid import taxes.
With current euro exchange rate and recent price increases i think prices are much less attractive. grey dealers in SG may give you better pricing (depending on the exact watch model). I think bags/leather goods still can buy bah.
If you want to buy watches overseas, need to plan in advance and email some ADs to ask about availability, otherwise you may hoot the wrong watch...