I almost stopped using the spline modeller, myself, for one of those problems. It has a strange ability to create visible breaks in the flow of the mesh where a cross-section was inserted. It also doesn't translate as smoothly into mesh as a polyline extruded or path swept within the vertex modeller (although you lose the ability to adjust both path and envelope, and to keep the thing editable, too). Better to say I stopped using the spline modeller for anything I was going to continue in the vertex modeller. It works great for stand-alone stuff (like all those set-dressing bits of cable, brackets, candlesticks, finials, crown moldings...) To select inside a model you could; a) select everything that's outside and hide the selection; b) go to wire-frame mode and click very carfully one by one; and sometimes you can c) set the right propagating selection angle and double-click on edges leading into the difficult zone -- Carrara will extend the selection along edges that lie along roughly the same line, and you can get into many corners that way.