Testpoints: Vias versus pads
I actually prefer vias as testpoints for just the reasons you mentioned. I think it makes using a multimeter or a scope probe much easier. Which, after all, is the main use of testpoints.

Where possible/practical, I like to size my vias large enough or use small plated through holes so that 30 gauge wire can easily be soldered in. Then I can clip a scope probe to the wire and have my hands completely free to operate a computer or other test equipment.

The reason not to use vias and especially not to tack wires on is the additional inductance and capacitance that such features would add to the trace and therefore distort your signal. This is of great importance when you're trying to measure high speed signals. Here is a good article on calculating via inductance.



$$L_1 = \dfrac{\mu}{2\pi}2h\cdot ln\dfrac{s}{r}$$

Where:
\$\mu = 4\pi\cdot10^{-7} H/m\$ - the magnetic permeability of free space
\$x\$ - the radial distance in meters away from the signal via
\$s\$ - the separation between vias, center-to-center
\$h\$ - the separation between planes 2 and 3
\$r\$ - the radius of the via holes  

Keep in mind that this formula makes some assumptions that the author notes and is therefore just an approximation:


  This formula for L? is a gross approximation that glosses over the
  position of the returning current path, a simplification I greatly
  regret not making more clear in the book. It makes the crude
  assumption that the return path is approximately coaxial and located
  at a distance s=2eh, where e is the base used for natural logarithms.
  When the inductance really matters, a more accurate approximation is
  needed.


However, the article Test Pads on High-Speed Nets points out the problems that that form of instrumentation can cause.


  If the signal is on an outer layer, it’s not possible to place a 35
  mil test pad directly on a 5 mil wide trace without creating a PCB
  routing nightmare. Differential signals are intended to be closely
  coupled, and the radius of the test pad will create additional routing
  constraints where they are already likely to be over-constrained:




Instead they recommend using non-intrusive technologies when trying to measure high speed signals. Which leads me to believe that, on signals that can handle the additional inductance and capacitance of a via, there is no reason to use a test pad given the benefits a via gives to using a meter or a probe.