I apologise in advance. I can't help it, but I was a Linn LP12 setter-upper from 1976 right into the noughties before I retired from HiFi retail...
One of the things that was drummed into 'us' was the correct procedure for vinyl system upgrades. The turntable itself always came first, followed by the tonearm and lastly the cartridge, followed by the phono stage, then amp and lastly the speakers. This hierarchy was easily demonstrated in the shop too, so I don't think this aspect was mere brainwash. Perhaps in the US this wasn't taken so seriously for a while, I don't know and of course there are better decks for getting music off records than an LP12 these days (usually new-car money and above though), though this latter springy belt drive has improved hugely over its life in both set-up and sonic/tonal neutrality without losing the 'listener involvement' aspect.
The systematic way above was abused hugely to the extreme by many UK dealers, putting an expensive Linn-style turntable with a low cost NAD amp and say, Wharfedale Diamond speakers (original Diamonds are great fun, but a bit 'extreme' here), but the theory was that if you lose or distort the musical information at the deck end, it doesn't matter how good the arm, cartridge, amp or speakers are, you'll never get it back! I've been ridiculed for saying this, but a humble AT95E cartridge could always sound surprisingly good when put on a decent top end turntable, despite it's almost give-away price. You may not want to keep the cartridge long term this way, but it's done many audiophiles great favours when their precious MC type has gone away for re-tipping or whatever.
With digital, you can now go back to the original way of thinking and put the speakers first in my experience as current cheapo DAC's costing ten quid (or less sometimes) actually 'sound' very fair indeed and don't go badly wrong at all, but with VINYL, you can't make these generalisations.
I'm bringing this up as a reminder to myself too. An old idler driven Dual can be a wonderful thing to behold and use, but 'wide dynamic range and no added noise' isn't always part of its portfolio (I'll make an exception with the 1219/1229 family as when new, as they were pretty darned quiet through the stylus to the speakers and I've never compared a 1209 to them I'm afraid). Look at the Dual specs and see how 'rumble' figures significantly reduced as the models evolved, rumble here being motor vibrations coming through as a kind of distant 'droning noise' as much as the far smaller 'rumble' in the main, often ball race, bearings, which were usually very good if lubed properly.
Dual tonearms in most cases from the 10** series onwards are perfectly serviceable for modern cartridges and quite incredible musically in the 1229 family, 601 and immediate descendants, 701 and 721, despite not 'measuring' as rigid as separate counterparts such as Rega RB models for example, these latter sounding grey and 'boring' if you get them wrong, offering some rigidity and usually very low friction. In fact I loved the 1019 when I first came by one thirty odd years ago as the large diameter pipe and non-perforated headshell reminded me of the Linn Ittok arm with large diameter pipe and others such as the Zeta and descended models. Discovering that this arm and its siblings could track really good mm cartridge types and *sound* really good while doing so and in fact wasn't quite as massive as it looked was a huge bonus for me, but at the end of the day, the TURNTABLE part including motor and idler drive governed everything simply by the noises this drive could impart if not running correctly and much of this being the idler itself after fifty years.
So to conclude this 'thinking out loud,' I'd urge buyers of some cheap 'thrift-store' lower Dual models (especially those with 4 pole and upwards motors on them) not to ditch a perfectly good tonearm (if understood and used correctly) and also possibly stiff mechanical parts which only need carefully servicing, but to look first at the motor, idler wheel and platter bearing, as iffy performance here will affect everything that comes afterwards. Directly bolting the deck frame to the plinth seems to make little difference here as the main source of transmitted vibration *seems* to come from a tired idler wheel or possible worn drive belt (although some belt drives need the motor looking at too). Dual arms were largely better engineered to those fitted to the average large-format Garrards, and ther performance can't be fully judged until the drive is working properly.
Does any of this make sense to you 'chaps?' I and others hold classic Duals so highly because they were able to extract the music from records so well in competition with other 'HiFi' integrated models, *despite* many of them basically being auto-changers - and auto-changers in the UK were sneered at from the mid 60's onwards for 'High Fidelity' use. Fortunately, 70's Duals with single-record spindles don't look especially like 'changers and I think this helped.