Retinoid:
NO your whole chart (rasi chart) is not spoiled due to navamsa placements, although these placements act as a modification, but then so do the drekkana placements and also the dwasdashima palcements as well; and of course the D30 and, ultimately, the D60 (karma varga) indications, show even deeper levels of life trends. These varga charts are much like the "harmonic" charts of certain approaches to Modernist astrology, and investigation into them (varga or "harmonic" charts) allows one to explore ever more deeply into trends/counter trends, and potentialities, beyond the obvious (ie, beyond the "original" natal-rasi-chart) In contemporary Vedic astrology, generally the rasi and navamsa charts are investigated, but Parasara (and others in the ancient past) urged that all the varga charts (divisional charts) be taken into consideration before final prognostication is made-quite a task!!
Sandstone:
A couple of informative books specifically about navamsa and divisional charts (varga charts, "Vedic harmonic charts")
+"Navamsa in Astrology" , C.S. Patel
+"Vargas: a Vedic Approach", R. Kumar
+"Predict Comprehensively through Divisional Charts", V.P. Goel
(these books generally available on the internet, specifically available from astroamerica.com)