Fultonius, I think that there is a small chance that your bouldering grade would actually improve (on the margin) if your aerobic power improved. Aerobic strength is still strength, and hypertrophy of type I muscle cells is hard to achieve without training somewhat aerobically. As long as you can protect the type II muscle cells from atrophy, improvement in aerobic strength will improve overall strength (by a little). I have seen this happen for boulder specialists after their first bout of endurance training.
