i thought about this post i as was climbing a nasty hill for the 4th repeat yesterday afternoon. I may be a little odd, but i have no problem doing tempo runs and fartlek during base training, as long as i stay at or just below lactic threshold. I wouldn't want to be anaerobic during base building (i.e. interval speed work or hill repeats) too much. But adding a hilly course and/or doing a few short bursts uphill or strides every few days I would think would only help with strengthening and adding to fitness, so long as it is done in moderation and under control. just my 2 cents.