Seems as the reason of the slowdown is the DataTable. It cannot be spatially indexed, thereby it will be processed fully on each map update. We recommend to use the original shapefile, indexed by the Spatial Index Builder, which is included with AspMap. This is the fastest method, comparing to any other.
Another solution is to export the shapefile into a spatial database and create a spatial index for the table (our Spatial Exporter tool does both tasks - http://www.vdstech.com/spatialexporter.aspx). The data in the spatial database table can be changed via AspMap or ADO.NET.
The video at http://youtu.be/K3etaYh1lBM still do not make it clear why such a simple task as enabling a layer takes so much time. It is recommended to submit a support ticket with the source code.