What are some incapabilities that the early spectroscopy have when compared to the more modern method?
Some of the things that come to mind are:


Resolution  Modern equipment has much higher resolution than older equipment.  Optical component surface smoothness and uniformity, optical component alignment and electrical component stability all permit the user to see more detail and fine structure in the spectrum, which assists in analysis
More stable light sources  Again resulting in more detailed and more reproducible spectra
Improved monochromaticity of the light sources  Further improving spectral resolution
Improved sample cells  Polished glass surfaces provide for better signal to noise making it easier to discern the signal
Signal processing software  Such as Fourier Transform methods which increase the signal to noise ratio making it easier to discern the true peaks in a spectrum
Other computer and software enhancements  That can be applied to sample handling and spectrum processing.  They dramatically reduce the time it takes to record and process a spectrum