As a former happy TC-50s owner, and if I thought they still sounded mint (over time mine got pretty dull sounding) AND needed another pair of speakers, I'd pay around $400 for them. In their day, those things really had unbelievable detail and soundstage- and sounded amazingly real for what they were. My first audiophile speakers...makes me wish I was setting up an additional room! I bet they'd be great with a sub and in a home theater setup too.

BTW- what do you mean by upgrade? Replaced older crossover parts? Something else?

Some have put in dynaudio woofers and similar in the same box, and then done some minor crossover mods. Maybe a different tweeter as well, like a scanspeak. Pretty common.

The tilted back box creates a situation where the beaming off the center of the woofer cone sprays upward instead of in your face,and thus the distortion components that reside above the combination of mechanical hysteresis and coil Q reacting against the q and hysteresis of the motor structure are less prominent and allow for a more gentle crossover slope with less reflective energies. You get a livelier acoustic field from the tiling back as reflects vs direct energies are different than a perpendicular (face of box) box design, thus affecting the overall energy balance in the room. This gentle slope allows for cleaner transients due to the above mentioned issues and how it gets handled. The mechanical alignment of the woofer and tweeter acoustic centers allows for better phase integration in the crossover range and harmonic overtones of bass note structure are integrated with the fundamentals and thus the speaker sounds tuneful and driven, ie, it makes your butt move with the music, the music is propelled along as it is phase integrated more closely - as it is in real life. This tends to sound a lot like electrostatic considerations through the midbass and up, and having the back of the box sealed kills the prominence of immediate reflections that can interfere in electrostatics, which tends to be one of the primary sources of the issues that makes some people not like the sound of electrostatics - or at least a part of what they don't like. The capacitor on a tweeter crossover and the inductor on the woofer crossover each skew the time delivery of the given note when attempting to reproduce the given note in the range of frequencies where the crossover is 'acting'. They go in opposite directions, with this change in the time of the signal delivery. So..the midband (~1.75kHz-~2.5kHz and up to maybe 4kHz) is phase or time skewed in comparison to the rest of the given note structure the whole system is attempting to reproduce.

The human ear is good at filtering and pulling intelligible date from complex signals and we automatically use this internal component of listening to 'gloss over' this mess of signal. To get to a point of really understanding what speakers and equipment do, is to learn to turn this automatic physical mechanism off, or on it's head.

What we do, almost to a person, is we derive signal from the peak values of signals and their differential as compared to any noise (of whatever nature).

Learning to shut off or listen past this automatic mechanism allows one to hear (and for most of us, for the first time) what is really going on. Our automatic system produces a bias of thinking that peak noise signals which are clearly delineated and separated from the main body of the signal can somehow constitute signal quality increases. Thus the people who have very tilted up systems,and they are living on the noise and interpreting that somehow as signal and ignoring the core issues..as that's the way they've been brought up to hear stuff on the hi-fi. In the most literal sense, we have ALL be brought up to hear things that way. Turing it around and going after the sublime and the fundamentally (and temporally, dynamically, etc) correct in the sonic presentation is something that does not happen to all of us and it actually concerns a small subset of the audiophile crowd, not the whole group. This is sad.

Anyway, point being, is that the original Spica TC-50 did and does simply one aspect of this essential point I'm trying to get across. As the components of how the ear and brain listens and interprets is not a big subject in the knowledge base of audiophiles and designers, this situation will exist for quite some time yet, and does definitely affect everything in the audio biz from microphone choices through to listening room acoustics for audiophiles.

The very ground that audiophiles walk on is not understood for being a problematic and misunderstood and misapplied critical component-ie, the mechanism of ear brain and how it is applied in audio design and execution, as stated, from the microphone to the listening chair.

Question the question.

If in excellent shape with no issues, like woofer sag..which is common in a spica TC-50, then they might command as much as $400, with the median being $275.

Add in the value of the subs, if they are the Kinergetics with the 2x 10" pr box and two boxes..and the amp, we are talking about $350-400 for those. You tend to get less for the two as a set rather than separately. Results vary!

A mint set of the subwoofers and amp went on ebay a while back for about $270, IIRC. But that's ebay.