I agree that it's possible to use Nagarjuna to assist one's understanding. Kalupahana seems to have been able to do this. But as Tilt pointed out, the madhyamika tradition (though perhaps not Nagarjuna himself) makes much larger claims as to the importance of their analysis. They do not consider madhyamika to be one among a number of possible interpretations. The view of madhyamika is that without an understanding of madhyamika one cannot awaken. I disagree with that and if Nagarjuna really meant that then I respectfully disagree with Nagarjuna.
Regarding the perception of the garden as a subtle emptiness, I don't think that is so. Perception does not, in itself, entail an ontological position. I can imagine a devout monotheist looking at the garden and feeling that the beauty of the garden is a sign of the beauty of the Lord, the Creator of All. This is not a view of subtle emptiness. Most people, I suspect, don't really give it much thought one way or the other, and there's something to be said for just getting down to the gardening.
Madhyamakans make the claim that emptiness is ontological and metaphysical (that there is
emptiness, and emptiness=form), whereas Theravadins make the claim that it is merely teleological and merely an extension of anatta and anicca (people should realize
emptiness, in the sense of impermanence and notself) .
However, as I've pointed out elsewhere, to say that there are "strategies for reducing suffering," well, such strategies don't exist in a vaccuum. In order for them to be effective, they have to be based upon reality. The Buddha spoke of both internal and
external sunnatta, which suggests that sunnatta isn't merely a mental property or fabrication. He also said in the Cula-suññata Sutta
, "And so this, his entry into emptiness, accords with actuality
So, I don't think there's really anything worth arguing over. If you emphasize sunatta as an ontological, metaphysical, philosophical concept, etc., there is the risk of it merely being papanca, manifesting using Buddhist terminology. However, if you emphasize sunnatta as purpose-driven, without acknowledging that it's a teaching based on reality or truth, then what you're saying can be seen as incoherent.
For Madhyamakins: If everything is sunnatta, then where is it?
(What is the cause for the apparent "suchness" and variety?)
For Theravadins: If there is no sunnatta, then how can sunnatta be realized?
Madhyamaka should not be misunderstood as nihilism, mysticism, or nonrealism, and Theravada should not be misunderstood as materialism, agnosticism, or a kind of realism.