I suspect you are getting limited value from Krisflyer.

If you are looking to redeem your miles for a short haul trip to Amsterdam you need to compare the amount Krisflyer will levy for taxes and surcharges on an award ticket against the best deal you can get purchasing the ticket online or from a discount travel agent.

Against that you also need to consider if you paid a higher fare than you needed to in order to earn the miles in your Krisflyer account.

LHR/SIN is fairly competitive and there are a number of reasonable carriers on this route. If you are only flying once every couple of years the best option might be to just focus on getting the best fare and ignore frequent flyer allegiance. The amount you save could easily be equal to the value of any benefit you receive via award flights.

If you have a particularly strong preference for flying SQ – fine, but you should also consider posting your miles to another Star Alliance frequent flyer scheme. Krisflyer’s 3 year limitation really seems to be working against you and your flight pattern. A better option might be a scheme where your points never expire (or require minimum account activity to keep them valid).

With your earning pattern a short haul flight to Europe or a side trip to SE Asia is about the best that you can achieve before your miles start to expire in the Krisflyer scheme. Better than nothing certainly, but both of these options are low value. Switching to a scheme that allows you to build up your miles over a longer period could give better value.